NATE CR Service cheat sheet

Superheat is the difference between the actual suction line temperature and the saturated evaporating temperature at the same pressure; measure both at the same point on the suction line.

Subcooling is the difference between the saturated condensing temperature and the actual liquid line temperature; typical values at full load are 8-15 °F for most commercial systems.

Target superheat at the evaporator outlet is typically 8-12 °F for a fixed-orifice (piston) system and 4-8 °F at the compressor inlet for a TEV system; a TEV maintains superheat by modulating refrigerant flow.

The pressure-temperature relationship is refrigerant-specific; R-404A, R-448A, R-449A, and R-507A have different glide and PT tables, so always use the correct PT chart or gauge for the specific refrigerant.

Zeotropic blends such as R-404A, R-407A, and R-448A have temperature glide; for these, use dew point for superheat and bubble point for subcooling calculations.

A low superheat reading at the compressor with normal evaporator superheat indicates liquid floodback; check for an overfed TEV, a stuck-open valve, or an oversized/incorrectly adjusted valve.

A high superheat with a starved evaporator indicates undercharge, a restricted liquid line filter-drier, a stuck-closed TEV, or a clogged screen at the valve inlet.

The compressor's rated capacity is published at ARI standard conditions; derate capacity for lower suction pressure (lower evaporating temperature) and higher condensing temperature using the manufacturer's performance tables.

Heat load on a walk-in cooler equals product load plus transmission load plus infiltration load plus internal (people, lights, motors) load; defrost and pull-down loads are added for sizing.

A liquid line filter-drier removes moisture and particulate; a pressure drop across the drier greater than 2-3 psi at full flow indicates restriction and replacement.

A sight glass with a moisture indicator shows bubbles if the liquid line is flashing; bubbles can indicate undercharge, a restriction, or insufficient subcooling, not always low charge.

A receiver stores liquid refrigerant; the liquid level should be sufficient to cover the dip tube outlet under all load conditions, typically at least 25% of the sight glass, or per manufacturer instructions.

A crankcase pressure-regulating (CPR) valve limits suction pressure at the compressor to prevent motor overload during pull-down or high evaporator load; set it per manufacturer's compressor rating.

An evaporator pressure-regulating (EPR) valve maintains a minimum evaporating pressure for one or more fixtures on a common suction line, preventing coil icing and product dehydration.

A defrost termination and fan delay (DTFD) control terminates defrost on temperature and delays evaporator fans until the coil is below a set temperature, preventing warm air from blowing on product.

A pump-down cycle uses a liquid line solenoid valve and low-pressure switch to pump the evaporator down and store refrigerant in the receiver, preventing liquid migration to the compressor during off cycles.

The low-pressure switch cut-out and cut-in settings must be set based on the refrigerant's pressure-temperature relationship and the desired minimum evaporator temperature; a too-low cut-out can cause coil icing.

An oil pressure safety (OPS) control trips the compressor when oil pressure fails to build within the time delay (typically 90-180 seconds) after startup, protecting against lubrication failure.

To calculate superheat: measure suction line temperature at the evaporator outlet and suction pressure at the same point; convert pressure to saturated temperature using the correct PT chart; subtract saturated temperature from line temperature.

To calculate subcooling: measure liquid line temperature at the condenser outlet and condensing pressure (or discharge pressure) at the same point; convert pressure to saturated temperature; subtract liquid line temperature from saturated temperature.

A compressor that runs continuously and does not pull down may be low on charge, have a restricted metering device, a dirty condenser, or a failed compressor valve; check superheat, subcooling, and amp draw before condemning the compressor.

A compressor that trips on overload shortly after startup may have a seized or grounded winding, a high head pressure from a dirty condenser or non-condensable gases, or a low voltage supply; check voltage and amp draw at startup.

Non-condensable gases in the system raise head pressure and cause high subcooling with high discharge temperature; purge or recover and recharge if found.

A dirty condenser raises condensing temperature and pressure, increasing compression ratio, reducing capacity, and raising amp draw; clean coils and check fan operation before diagnosing other faults.

A restricted capillary tube or TEV can cause low suction pressure and low superheat at the evaporator but high superheat at the compressor if the restriction is at the inlet screen.

Ice formation on the evaporator can be caused by a defrost failure, a failed defrost heater, a bad DTFD, low refrigerant charge, or a restricted airflow; diagnose by checking defrost cycle operation and coil temperature.

Recovery of refrigerant is required before opening a system to atmosphere; use EPA Section 608 recovery equipment and follow evacuation to 500 microns for a tight system before recharging.

ASHRAE safety group classifications: A1 refrigerants (R-404A, R-507A, R-134a) have low toxicity and no flame propagation; A2L refrigerants (R-454A, R-454C, R-455A) have low toxicity and lower flammability.

R-404A has a GWP of approximately 3,922; R-448A and R-449A have GWP around 1,273-1,397, making them common lower-GWP retrofits for R-404A systems.

R-22 is an HCFC with an ozone depletion potential of 0.055; production and import are phased out in the U.S., and only recovered/reclaimed R-22 may be used for service.

Refrigerant cylinders must never be filled above 80% of their capacity by volume; use a scale and follow DOT and EPA requirements for transport.

Nitrogen is used for pressure testing and leak detection; never use oxygen or air in a refrigeration system, as it can cause an explosion when combined with oil.

A refrigerant leak in an occupied space can displace oxygen; ventilate the area and use a refrigerant detector before entering; A2L refrigerants also require ignition-source control and leak detection per ASHRAE 15.

Evacuation to 500 microns and a standing vacuum test (holding below 1,000 microns for 10-15 minutes) verifies a tight, dry system before charging.

Charging by weight is the most accurate method for systems with a receiver; charging by superheat or subcooling is used when the nameplate charge is unknown.

A potential relay in a single-phase compressor uses the back-EMF from the start winding to open the start capacitor circuit once the motor reaches approximately 75% speed.

A current relay operates on the compressor's running current; its contacts close during startup to energize the start winding and open when current drops as the motor accelerates.

A PTC (positive temperature coefficient) start device increases resistance as it heats, reducing start winding current after startup; it is common on small hermetic compressors.

The compressor run capacitor improves power factor and motor efficiency; a failed run capacitor causes high amp draw and overheating.

A contactor's coil voltage must match the control circuit voltage; a chattering contactor often indicates low control voltage or a loose connection.

A defrost timer or control board initiates defrost cycles based on time and temperature; verify the timer motor is advancing and the termination switch opens at the correct temperature.

Motor winding resistance should be checked with a meter; a grounded winding shows continuity from winding to the compressor shell, and an open winding shows infinite resistance.

A compressor's locked rotor amps (LRA) is typically 5-7 times the rated load amps (RLA); a compressor drawing LRA without starting indicates a mechanical or electrical failure.

Cooler design temperature is typically 35-38 °F for product storage; freezer design temperature is typically 0 °F or lower, with evaporator temperature 10-15 °F below the box temperature.

The refrigeration load includes product load (specific heat and latent heat of freezing), transmission load through walls (U-factor × area × temperature difference), infiltration (door openings), and internal loads (lights, fans, people).

The evaporator TD (temperature difference between box and evaporator) is typically 10 °F for coolers and 10-15 °F for freezers; a higher TD increases capacity but lowers humidity and increases coil frost.

A larger condenser TD (condensing temperature minus ambient) increases capacity but raises head pressure and energy use; typical design TD is 10-15 °F for air-cooled condensers.

Line sizing must maintain adequate refrigerant velocity to return oil to the compressor while limiting pressure drop; horizontal suction lines should slope toward the compressor at about 1/4 inch per 10 feet.

A P-trap at the base of a suction riser returns oil to the compressor; an inverted trap at the top prevents oil from draining back into the evaporator during off cycles.

The receiver must be sized to hold the entire system charge plus a 10-15% margin; an undersized receiver causes high head pressure and poor subcooling.

A liquid line solenoid valve in a pump-down system must be sized for the full liquid flow rate and located close to the evaporator to minimize pump-down time.

Record suction and discharge pressures, superheat, subcooling, ambient temperature, box temperature, and compressor amp draw at each PM visit to trend performance over time.

Clean condenser coils at least quarterly; a dirty coil raises head pressure, increases amp draw, and reduces capacity.

Check and replace liquid line filter-driers when pressure drop exceeds 2-3 psi or the moisture indicator shows moisture.

Verify defrost termination temperature and fan delay settings; a defrost that terminates too early leaves frost, and one that runs too long raises box temperature.

Check door gaskets and closers; a leaking gasket causes infiltration, icing, and increased load.

Verify refrigerant charge by weight or by subcooling/superheat; do not top off a system without identifying the leak source.

Check electrical connections for tightness and signs of overheating; loose connections cause voltage drop and compressor failure.

Document refrigerant added, recovered, or recycled per EPA Section 608 requirements, including the date, amount, and reason.

Technicians who service or dispose of appliances containing refrigerant must hold EPA Section 608 certification; Type I covers small appliances, Type II covers high-pressure systems, and Type III covers low-pressure systems.

Refrigerant may not be knowingly vented to the atmosphere during service, maintenance, or disposal; use certified recovery equipment.

Recovery cylinders must be DOT-approved and never filled above 80% of capacity by volume.

Appliances with a charge of 5 pounds or more must be evacuated to 0 inches of mercury before opening, and to 10 inches of mercury for systems with a charge of less than 5 pounds, per EPA requirements for high-pressure appliances.

A refrigerant leak in an appliance with a charge of 50 pounds or more must be repaired within 30 days if the leak rate exceeds the applicable threshold; chronic leakers may require retrofit or retirement.

Reclaimed refrigerant must meet ARI 700 purity standards before it can be resold or used in another appliance.

When retrofitting R-22 to a HFC blend, the mineral oil must be replaced with POE oil or a compatible lubricant; residual mineral oil can cause oil return problems.

R-448A and R-449A are common R-404A retrofits; they require checking elastomer seals, filter-drier compatibility, and TXV orifice sizing because of different capacity and glide.

Zeotropic blends require charging as a liquid to prevent fractionation; charge by weight and use the dew point for superheat and bubble point for subcooling.

After a retrofit, the system's pressure controls (low-pressure switch, high-pressure switch, EPR, CPR) must be reset to the new refrigerant's pressure-temperature relationship.

A retrofit should include replacing the filter-drier, checking for leaks, and verifying oil return with a sight glass or oil level check after startup.

Capacity and efficiency may change after a retrofit; check compressor amp draw against nameplate and adjust charge to achieve target superheat and subcooling.

A walk-in cooler with a box temperature above design and a normal superheat may have a failed evaporator fan, a frosted coil, or a door left open; check airflow and coil condition first.

A freezer with ice on the ceiling or floor often has a defrost problem, a failed defrost heater, or a bad termination switch; verify heater resistance and termination temperature.

A walk-in with a warm box and a compressor that runs continuously but has low suction pressure and high superheat may be low on charge or have a restricted liquid line.

Check the evaporator fan blades for ice buildup and the fan motor for proper rotation; a fan running backward reduces airflow and capacity.

Verify the door heater and frame heater are working; a failed heater causes condensation and ice on the door frame.

The defrost cycle should be set based on the box's frost accumulation; too-frequent defrosts raise box temperature, and too-infrequent defrosts cause coil icing.

Check the drain line and drain pan heater; a clogged or unheated drain causes ice buildup at the evaporator.

An ice machine that produces cloudy or soft ice may have a water quality issue, a dirty evaporator, or a failed water filter; check water hardness and filter condition.

A cube ice machine that does not harvest may have a failed harvest cycle, a bad bin switch, or a hot gas valve that is not opening; verify the harvest initiation and hot gas valve operation.

Ice machine capacity depends on ambient air and inlet water temperature; capacity drops as either temperature rises, so verify conditions against the manufacturer's ratings.

The ice machine's condenser must be cleaned regularly; a dirty condenser reduces capacity and can cause the machine to shut down on high pressure.

A flake ice machine uses an auger and a gear motor; a jammed auger or a failed gear motor stops ice production.

Water filters should be replaced per the manufacturer's schedule or when the pressure drop across the filter exceeds the recommended limit.

The refrigeration cycle has four main components: compressor, condenser, metering device, and evaporator; the compressor raises pressure and temperature, the condenser rejects heat, the metering device drops pressure, and the evaporator absorbs heat.

The compressor's suction side is the low-pressure side; the discharge side is the high-pressure side; the liquid line is high pressure and the suction line is low pressure.

The condenser removes sensible heat (desuperheating) and latent heat (condensing) from the refrigerant; subcooling occurs after the refrigerant is fully liquid.

The evaporator absorbs heat from the space; superheat occurs after the refrigerant is fully vaporized, protecting the compressor from liquid slugging.

The metering device maintains the pressure difference between the high and low sides and regulates refrigerant flow to the evaporator.

A compressor's compression ratio is the absolute discharge pressure divided by the absolute suction pressure; a high ratio reduces capacity and raises discharge temperature.

The refrigerant's latent heat of vaporization determines how much heat the evaporator can absorb per pound of refrigerant; it varies by refrigerant.

A manifold gauge set with the correct refrigerant hoses and gauges is required for each refrigerant; never use a gauge set rated for a different refrigerant without verifying compatibility.

A digital thermometer or thermocouple with a clamp is used to measure line temperature for superheat and subcooling; accuracy within 1 °F is needed.

A vacuum gauge (micron gauge) must be used to verify evacuation; a manifold gauge is not accurate enough for micron readings.

A refrigerant leak detector should be calibrated and tested before each use; electronic detectors are sensitive to airflow and should be moved slowly along joints.

A clamp-on ammeter measures compressor amp draw; compare to nameplate RLA and LRA to diagnose electrical problems.

A multimeter is used to check voltage, resistance, and continuity; a capacitor tester checks run and start capacitors.

A refrigerant recovery machine and DOT-approved recovery cylinder are required for service; never use a recovery cylinder for anything other than refrigerant.

High head pressure with high subcooling: dirty condenser, non-condensable gases, or overcharge; check condenser airflow and subcooling.

High head pressure with low subcooling: undercharge or a restriction; check for bubbles in the sight glass and superheat.

Low suction pressure with high superheat: undercharge, restricted liquid line, or a stuck-closed TEV; check superheat at the evaporator.

Low suction pressure with low superheat: overfed evaporator, stuck-open TEV, or a failed compressor valve; check superheat at the compressor.

Compressor runs but does not cool: check for a failed compressor valve, low charge, or a restricted metering device; verify suction and discharge pressures.

Compressor trips on overload: check for high head pressure, low voltage, a failed run capacitor, or a seized compressor.

Ice on the suction line: low charge or a restricted TEV; check superheat and subcooling.

Box temperature too warm with normal pressures: check airflow, door seals, defrost operation, and product load.

Charge by weight when the nameplate charge is known; use a scale accurate to 0.1 ounce for small systems and 1 ounce for larger systems.

When charging by superheat, add refrigerant until superheat reaches the target for the current ambient and box temperature; never charge to a fixed superheat without verifying conditions.

When charging by subcooling, add refrigerant until subcooling reaches the target (typically 8-15 °F); subcooling is the preferred method for systems with a receiver and TEV.

Overcharging raises head pressure and subcooling and can cause liquid floodback; undercharging raises superheat and reduces capacity.

After charging, verify the sight glass is clear (no bubbles) and the moisture indicator is dry.

Record the final charge, superheat, subcooling, and pressures on the service ticket for future reference.

Reciprocating compressors use pistons and valves; they are common in small and medium commercial systems and can be semi-hermetic or hermetic.

Scroll compressors use two intermeshing scrolls; they are common in larger systems and have fewer moving parts than reciprocating compressors.

Screw compressors use two rotors and are used in large industrial systems; they have high capacity and continuous compression.

A semi-hermetic compressor can be rebuilt; a hermetic compressor is welded and is typically replaced rather than repaired.

Compressor valve failure causes low capacity, high discharge temperature, and abnormal suction/discharge pressure relationships; verify with a pump-down test or valve plate inspection.

Compressor oil level should be checked at the sight glass; low oil indicates oil return problems or a leak.

Acid in the system from a compressor burnout requires a suction line filter-drier and oil change; test oil with an acid test kit.

Air-cooled condensers reject heat to ambient air; the condensing temperature is typically 10-15 °F above ambient.

Water-cooled condensers use water or a cooling tower; they require water treatment to prevent scale and corrosion.

Evaporator coils should be cleaned regularly; a dirty coil reduces heat transfer and raises superheat.

Evaporator fan motors should be checked for proper rotation and amp draw; a failed fan causes coil icing and poor capacity.

The evaporator's TD (box temperature minus evaporating temperature) affects humidity; a higher TD lowers humidity but increases frost.

Condenser subcooling circuits (subcoolers) increase subcooling and system efficiency; they must be checked for proper refrigerant flow.

Coil fin damage reduces airflow and heat transfer; comb fins straight and replace damaged coils.

Electric defrost uses heater elements in the evaporator; it is common in freezers and requires a defrost termination switch to prevent overheating.

Hot gas defrost uses hot discharge gas to melt frost; it is common in larger systems and requires a defrost differential valve and a termination control.

Off-cycle defrost relies on the compressor stopping and the coil warming above freezing; it is common in coolers and requires a defrost timer.

Defrost termination temperature is typically 45-55 °F for electric defrost; the switch opens when the coil reaches that temperature.

Fan delay settings keep evaporator fans off until the coil is below about 35 °F, preventing warm air from blowing on product.

A failed defrost heater, termination switch, or timer causes ice buildup; check heater resistance and switch continuity.

Defrost frequency should match frost accumulation; too-frequent defrosts waste energy and raise box temperature.

Evacuate to 500 microns and hold for 10-15 minutes; a rising vacuum indicates moisture or a leak.

Use a micron gauge at the system, not at the pump, to measure vacuum accurately.

Triple evacuation (evacuate, break with nitrogen, evacuate again) removes moisture and non-condensables.

Leak detection methods include electronic detectors, soap bubbles, ultraviolet dye, and pressure testing with nitrogen.

Never use oxygen or air for pressure testing; use dry nitrogen and a pressure regulator.

A system that will not hold vacuum has a leak or moisture; locate and repair before charging.

After repair, replace the filter-drier and evacuate again before recharging.

Lock out and tag out the power source before servicing electrical components; verify power is off with a meter.

Use a meter rated for the voltage and category of the circuit being tested.

Capacitors can hold a charge after power is removed; discharge them before handling.

Verify the compressor is off and the control circuit is de-energized before opening the compressor terminal box.

Use insulated tools and wear appropriate PPE when working on live circuits.

Check for proper grounding and bonding of the equipment; a missing ground is a shock hazard.

Follow NFPA 70E for arc flash and electrical safety requirements.

A thermostat cycles the compressor or a solenoid valve to maintain box temperature; check the setpoint and differential.

A pressure control can be used instead of a thermostat for pump-down or low-ambient operation.

An electronic controller may control temperature, defrost, and alarms; verify sensor placement and calibration.

A solenoid valve in the liquid line controls refrigerant flow to the evaporator; a stuck valve causes no cooling or floodback.

A hot gas bypass valve modulates capacity on systems with varying load; check for proper adjustment and operation.

A time delay relay prevents short cycling of the compressor; check the delay setting and relay operation.

Alarm systems should be tested regularly; a failed alarm can lead to product loss.

Suction lines should be sized to minimize pressure drop while maintaining oil return velocity; a pressure drop greater than 2 °F equivalent is excessive.

Liquid lines should be sized to minimize pressure drop and prevent flashing; subcooling helps prevent flashing.

Discharge lines should be sized to minimize pressure drop and maintain oil return; a discharge line trap at the compressor prevents oil from draining back during off cycles.

Suction risers should be sized for oil return at minimum load; a double riser may be used for systems with wide load variation.

Horizontal suction lines should slope toward the compressor at about 1/4 inch per 10 feet.

Piping should be supported and insulated; suction lines should be insulated to prevent condensation and heat gain.

Brazing should use dry nitrogen purge to prevent oxidation inside the piping.

Recovery equipment must be certified to ARI 740; use the correct recovery cylinder for the refrigerant type.

Recovery cylinders must be evacuated before use and never filled above 80% by volume.

Recovered refrigerant may be recycled or reclaimed; reclaimed refrigerant must meet ARI 700 standards.

Never mix refrigerants in a recovery cylinder; mixing makes reclamation impossible.

Label recovery cylinders with the refrigerant type and date.

Follow EPA Section 608 requirements for recovery, recycling, and disposal.

Use a scale to monitor the amount of refrigerant recovered and to avoid overfilling the cylinder.

Before startup, verify the system is evacuated, charged, and all valves are in the correct position.

Check the compressor oil level and rotation; a scroll compressor running backward will not pump.

Verify the condenser fan and evaporator fan rotation and amp draw.

Check the control settings, including thermostat setpoint, defrost timer, and pressure controls.

Record initial pressures, temperatures, superheat, subcooling, and amp draw.

Verify the system pulls down to the design temperature and cycles properly.

Check for leaks and proper refrigerant charge after the system stabilizes.

R-404A is an A1 refrigerant with a GWP of about 3,922; it is being phased down under EPA regulations.

R-448A and R-449A are A1 refrigerants with GWP around 1,273-1,397; they are common R-404A retrofits.

R-454A and R-454C are A2L refrigerants with lower GWP; they require ignition-source control and leak detection.

R-290 (propane) is an A3 refrigerant with high flammability; it is used in small self-contained units and requires specific safety measures.

R-744 (CO2) operates at high pressure and requires special equipment; it is used in transcritical systems.

Always consult the refrigerant's safety data sheet (SDS) for toxicity, flammability, and handling requirements.

Use personal protective equipment, including gloves and eye protection, when handling refrigerants.

Cycling the compressor on and off is the simplest capacity control; it is used on small systems with stable loads.

Hot gas bypass modulates capacity by injecting hot gas into the evaporator; it is used on systems with varying loads.

Cylinder unloading on reciprocating compressors reduces capacity by holding suction valves open; it is used on larger systems.

Variable-speed compressors modulate capacity by changing speed; they are used in modern systems for efficiency.

Electronic expansion valves (EEVs) modulate refrigerant flow based on superheat and other inputs; they offer precise control.

Multiple compressors or compressor racks allow staged capacity control; they are common in supermarkets.

Check the capacity control settings and operation during service to ensure proper modulation.

EPA Section 608 requires repair of leaks in appliances with a charge of 50 pounds or more when the leak rate exceeds the applicable threshold.

The leak rate is calculated as the amount of refrigerant added over a 12-month period divided by the appliance charge.

Repairs must be completed within 30 days of discovery; an extension may be requested if parts are unavailable.

Chronic leakers may require retrofit or retirement if they cannot be repaired.

Verify repairs with a follow-up leak test and document the results.

Keep records of leak repairs, refrigerant added, and the leak rate calculation.

Store refrigerant cylinders upright and secured; do not expose them to heat or direct sunlight.

Never fill a cylinder above 80% of its capacity by volume; use a scale to verify.

Use the correct cylinder for the refrigerant; never mix refrigerants.

Cylinders must be DOT-approved and inspected periodically.

Transport cylinders with valve caps installed and secured in a vehicle.

Do not use a cylinder as a support or roller; damage can cause a rupture.

Follow the manufacturer's instructions for filling and handling cylinders.

Moisture in a system forms acids and sludge, which can damage the compressor; use a filter-drier and evacuate properly.

Non-condensable gases raise head pressure and reduce capacity; purge or recover and recharge.

Acid in the system from a burnout requires a suction line filter-drier and oil change; test oil with an acid test kit.

Air in the system can cause high discharge temperature and pressure; evacuate properly before charging.

Contaminated refrigerant should be reclaimed or disposed of properly; never vent it.

Use a refrigerant identifier to check for mixed refrigerants before recovery.

Replace the filter-drier after any repair that opens the system.

Recover the existing refrigerant and properly dispose of or reclaim it.

Replace the filter-drier and any elastomer seals that are not compatible with the new refrigerant.

Check the lubricant compatibility; POE oil is required for most HFC blends.

Evacuate the system to 500 microns and hold to verify a tight, dry system.

Charge the new refrigerant by weight as a liquid to prevent fractionation.

Adjust pressure controls and verify superheat and subcooling.

Document the retrofit, including the new refrigerant type and charge.

Recovery machines must be certified to ARI 740 and used according to the manufacturer's instructions.

Use a recovery cylinder that is rated for the refrigerant and in good condition.

Recover refrigerant into a liquid phase when possible to speed recovery.

Use a scale to monitor the amount recovered and avoid overfilling.

Never use a recovery machine on a system with a flammable refrigerant unless the machine is rated for it.

Follow EPA requirements for recovery and recycling.

Label recovery cylinders with the refrigerant type and date.

ASHRAE Standard 34 classifies refrigerants by toxicity (A or B) and flammability (1, 2, 3).

A1 refrigerants have low toxicity and no flame propagation; examples include R-404A, R-134a, and R-410A.

A2L refrigerants have low toxicity and lower flammability; examples include R-454A, R-454C, and R-455A.

A3 refrigerants have low toxicity and high flammability; examples include R-290 (propane).

B1 refrigerants have higher toxicity and no flame propagation; examples include R-123.

B2 refrigerants have higher toxicity and lower flammability; examples include R-717 (ammonia).

Always consult the SDS and ASHRAE 34 for the specific refrigerant's classification.

The Montreal Protocol phases out ozone-depleting substances, including HCFCs such as R-22.

The Kigali Amendment phases down HFCs, including R-404A and R-134a.

The EPA's AIM Act implements the HFC phase-down in the U.S., with production and import allowances declining over time.

R-22 production and import are phased out in the U.S.; only recovered/reclaimed R-22 may be used for service.

R-404A has a high GWP and is being replaced by lower-GWP refrigerants such as R-448A and R-449A.

Compliance with refrigerant regulations requires recordkeeping and proper recovery and disposal.

Check current EPA regulations for specific requirements and deadlines.

Electronic leak detectors are sensitive to small leaks; calibrate and test before use.

Soap bubbles are useful for confirming a leak found with an electronic detector.

Ultraviolet dye can be added to the system to trace leaks; use only dye approved for the system.

Pressure testing with dry nitrogen can reveal leaks; never use oxygen or air.

Ultrasonic leak detectors can detect leaks in noisy environments.

A system that will not hold vacuum has a leak or moisture; locate and repair before charging.

Follow the manufacturer's instructions for the leak detection method used.

Charge by weight when the nameplate charge is known; use a scale accurate to 0.1 ounce for small systems.

Charge by superheat when the nameplate charge is unknown and the system has a fixed orifice; add refrigerant until superheat reaches the target.

Charge by subcooling when the system has a TEV and a receiver; add refrigerant until subcooling reaches the target.

Never charge a system with a flammable refrigerant without following the manufacturer's safety procedures.

Verify the charge with a sight glass and moisture indicator.

Record the final charge and system readings.

Use DOT-approved recovery cylinders and never fill above 80% by volume.

Evacuate recovery cylinders before use.

Label cylinders with the refrigerant type and date.

Store cylinders upright and secured; do not expose to heat.

Transport cylinders with valve caps installed and secured.

Never mix refrigerants in a recovery cylinder.

Follow EPA and DOT requirements for handling and transport.

Recycling removes oil, moisture, and particulates from refrigerant; it does not restore to ARI 700 purity.

Reclamation restores refrigerant to ARI 700 purity; it requires specialized equipment.

Reclaimed refrigerant can be resold and used in another appliance.

Recovered refrigerant that is not recycled or reclaimed must be disposed of properly.

Never vent refrigerant to the atmosphere.

Keep records of refrigerant recovered, recycled, and reclaimed.

Follow EPA Section 608 requirements for recycling and reclamation.

Wear gloves and eye protection when handling refrigerants; liquid refrigerant can cause frostbite.

Work in a well-ventilated area; refrigerant vapors can displace oxygen.

Do not allow refrigerant to contact open flames; it can decompose into toxic gases.

Use a refrigerant detector in enclosed spaces before entering.

Follow the SDS for the specific refrigerant.

Store cylinders in a cool, dry, well-ventilated area.

Never use refrigerant to clean equipment or as a propellant.

The compressor raises the pressure and temperature of the refrigerant vapor.

The condenser rejects heat from the refrigerant to the ambient air or water.

The metering device reduces the pressure and temperature of the refrigerant.

The evaporator absorbs heat from the space into the refrigerant.

The receiver stores liquid refrigerant and ensures a steady supply to the metering device.

The filter-drier removes moisture and particulate from the refrigerant.

The sight glass indicates refrigerant charge and moisture content.

The thermostat controls the box temperature by cycling the compressor or a solenoid valve.

The low-pressure switch protects the compressor from low suction pressure and controls pump-down.

The high-pressure switch protects the system from excessive discharge pressure.

The oil pressure safety switch protects the compressor from lubrication failure.

The defrost timer controls the defrost cycle.

The defrost termination switch ends the defrost cycle when the coil reaches the set temperature.

The fan delay switch delays the evaporator fans after defrost.

High head pressure: dirty condenser, non-condensable gases, overcharge, or high ambient.

Low head pressure: undercharge, low ambient, or a failed compressor.

High suction pressure: overcharge, high load, or a failed compressor valve.

Low suction pressure: undercharge, restriction, or a failed metering device.

High superheat: undercharge, restriction, or a stuck-closed TEV.

Low superheat: overcharge, overfed evaporator, or a stuck-open TEV.

High subcooling: overcharge or non-condensable gases.

Low subcooling: undercharge or a restriction.

Evacuate to 500 microns and hold for 10-15 minutes to verify a tight, dry system.

Use a micron gauge at the system, not at the pump.

Triple evacuation removes moisture and non-condensables.

Never use the system compressor to evacuate the system.

Replace the filter-drier before evacuation.

Check for leaks if the vacuum does not hold.

Charge the system only after a successful evacuation.

Use dry nitrogen for pressure testing; never use oxygen or air.

Pressurize the system to the manufacturer's recommended test pressure.

Use an electronic leak detector or soap bubbles to locate leaks.

Repair leaks and retest before charging.

Replace the filter-drier after any repair that opens the system.

Evacuate the system after repair.

Document the leak test and repair.

Charge by weight when the nameplate charge is known.

Charge by superheat or subcooling when the nameplate charge is unknown.

Never charge liquid refrigerant into the suction line of a running compressor.

Use a scale to monitor the charge.

Verify the charge with a sight glass and moisture indicator.

Record the final charge and system readings.

Check for leaks after charging.

Verify the system is evacuated and charged.

Check the compressor oil level and rotation.

Verify the condenser and evaporator fan rotation.

Check the control settings.

Record initial pressures, temperatures, superheat, subcooling, and amp draw.

Verify the system pulls down to the design temperature.

Check for leaks and proper charge after the system stabilizes.

Clean condenser coils regularly.

Check and replace filter-driers when pressure drop exceeds 2-3 psi.

Verify defrost termination and fan delay settings.

Check door gaskets and closers.

Verify refrigerant charge by weight or by subcooling/superheat.

Check electrical connections for tightness.

Document refrigerant added, recovered, or recycled.

Cooler design temperature is typically 35-38 °F.

Freezer design temperature is typically 0 °F or lower.

Evaporator TD is typically 10 °F for coolers and 10-15 °F for freezers.

Condenser TD is typically 10-15 °F.

Suction lines should be sized for oil return and minimal pressure drop.

A P-trap at the base of a suction riser returns oil to the compressor.

The receiver must be sized to hold the entire system charge plus a 10-15% margin.

Lock out and tag out the power source before servicing.

Use a meter rated for the voltage and category.

Discharge capacitors before handling.

Verify the compressor is off before opening the terminal box.

Use insulated tools and PPE.

Check for proper grounding and bonding.

Follow NFPA 70E for electrical safety.

Manifold gauge set with correct hoses and gauges.

Digital thermometer or thermocouple for superheat and subcooling.

Vacuum gauge (micron gauge) for evacuation.

Refrigerant leak detector.

Clamp-on ammeter for compressor amp draw.

Multimeter for voltage, resistance, and continuity.

Refrigerant recovery machine and DOT-approved recovery cylinder.

High head pressure with high subcooling: dirty condenser, non-condensable gases, or overcharge.

High head pressure with low subcooling: undercharge or a restriction.

Low suction pressure with high superheat: undercharge, restricted liquid line, or stuck-closed TEV.

Low suction pressure with low superheat: overfed evaporator, stuck-open TEV, or failed compressor valve.

Compressor runs but does not cool: failed compressor valve, low charge, or restricted metering device.

Compressor trips on overload: high head pressure, low voltage, failed run capacitor, or seized compressor.

Ice on suction line: low charge or restricted TEV.

Charge by weight when the nameplate charge is known.

Charge by superheat when the nameplate charge is unknown and the system has a fixed orifice.

Charge by subcooling when the system has a TEV and a receiver.

Overcharging raises head pressure and subcooling.

Undercharging raises superheat and reduces capacity.

Verify the sight glass is clear after charging.

Record the final charge and system readings.

Reciprocating compressors use pistons and valves.

Scroll compressors use two intermeshing scrolls.

Screw compressors use two rotors.

Semi-hermetic compressors can be rebuilt.

Hermetic compressors are welded and typically replaced.

Compressor valve failure causes low capacity and high discharge temperature.

Low oil indicates oil return problems or a leak.

Air-cooled condensers reject heat to ambient air.

Water-cooled condensers use water or a cooling tower.

Evaporator coils should be cleaned regularly.

Evaporator fan motors should be checked for proper rotation.

The evaporator TD affects humidity.

Condenser subcooling circuits increase subcooling.

Coil fin damage reduces airflow and heat transfer.

Electric defrost uses heater elements in the evaporator.

Hot gas defrost uses hot discharge gas to melt frost.

Off-cycle defrost relies on the compressor stopping.

Defrost termination temperature is typically 45-55 °F for electric defrost.

Fan delay settings keep evaporator fans off until the coil is below about 35 °F.

A failed defrost heater, termination switch, or timer causes ice buildup.

Defrost frequency should match frost accumulation.

Evacuate to 500 microns and hold for 10-15 minutes.

Use a micron gauge at the system.

Triple evacuation removes moisture and non-condensables.

Leak detection methods include electronic detectors, soap bubbles, ultraviolet dye, and pressure testing with nitrogen.

Never use oxygen or air for pressure testing.

A system that will not hold vacuum has a leak or moisture.

Replace the filter-drier after repair.

Lock out and tag out the power source before servicing.

Use a meter rated for the voltage and category.

Discharge capacitors before handling.

Verify the compressor is off before opening the terminal box.

Use insulated tools and PPE.

Check for proper grounding and bonding.

Follow NFPA 70E for electrical safety.

A thermostat cycles the compressor or a solenoid valve.

A pressure control can be used for pump-down or low-ambient operation.

An electronic controller may control temperature, defrost, and alarms.

A solenoid valve controls refrigerant flow to the evaporator.

A hot gas bypass valve modulates capacity.

A time delay relay prevents short cycling.

Alarm systems should be tested regularly.

Suction lines should minimize pressure drop while maintaining oil return velocity.

Liquid lines should minimize pressure drop and prevent flashing.

Discharge lines should minimize pressure drop and maintain oil return.

Suction risers should be sized for oil return at minimum load.

Horizontal suction lines should slope toward the compressor.

Piping should be supported and insulated.

Brazing should use dry nitrogen purge.

Recovery equipment must be certified to ARI 740.

Use the correct recovery cylinder for the refrigerant type.

Recovery cylinders must be evacuated before use.

Never fill above 80% by volume.

Recovered refrigerant may be recycled or reclaimed.

Never mix refrigerants in a recovery cylinder.

Label recovery cylinders with the refrigerant type and date.

Verify the system is evacuated, charged, and all valves are in the correct position.

Check the compressor oil level and rotation.

Verify the condenser fan and evaporator fan rotation and amp draw.

Check the control settings.

Record initial pressures, temperatures, superheat, subcooling, and amp draw.

Verify the system pulls down to the design temperature.

Check for leaks and proper charge after the system stabilizes.

R-404A is an A1 refrigerant with a GWP of about 3,922.

R-448A and R-449A are A1 refrigerants with GWP around 1,273-1,397.

R-454A and R-454C are A2L refrigerants with lower GWP.

R-290 (propane) is an A3 refrigerant with high flammability.

R-744 (CO2) operates at high pressure.

Always consult the SDS for the specific refrigerant.

Use PPE when handling refrigerants.

Cycling the compressor on and off is the simplest capacity control.

Hot gas bypass modulates capacity by injecting hot gas into the evaporator.

Cylinder unloading reduces capacity by holding suction valves open.

Variable-speed compressors modulate capacity by changing speed.

Electronic expansion valves modulate refrigerant flow based on superheat.

Multiple compressors or compressor racks allow staged capacity control.

Check the capacity control settings during service.

EPA Section 608 requires repair of leaks in appliances with a charge of 50 pounds or more when the leak rate exceeds the applicable threshold.

The leak rate is calculated as the amount of refrigerant added over a 12-month period divided by the appliance charge.

Repairs must be completed within 30 days of discovery.

Chronic leakers may require retrofit or retirement.

Verify repairs with a follow-up leak test.

Keep records of leak repairs and refrigerant added.

Store refrigerant cylinders upright and secured.

Never fill a cylinder above 80% of its capacity by volume.

Use the correct cylinder for the refrigerant.

Cylinders must be DOT-approved and inspected periodically.

Transport cylinders with valve caps installed.

Do not use a cylinder as a support or roller.

Follow the manufacturer's instructions for filling and handling.

Moisture in a system forms acids and sludge.

Non-condensable gases raise head pressure and reduce capacity.

Acid in the system from a burnout requires a suction line filter-drier and oil change.

Air in the system can cause high discharge temperature and pressure.

Contaminated refrigerant should be reclaimed or disposed of properly.

Use a refrigerant identifier to check for mixed refrigerants.

Replace the filter-drier after any repair that opens the system.

Recover the existing refrigerant and properly dispose of or reclaim it.

Replace the filter-drier and any incompatible elastomer seals.

Check the lubricant compatibility; POE oil is required for most HFC blends.

Evacuate the system to 500 microns and hold.

Charge the new refrigerant by weight as a liquid.

Adjust pressure controls and verify superheat and subcooling.

Document the retrofit.

Recovery machines must be certified to ARI 740.

Use a recovery cylinder rated for the refrigerant.

Recover refrigerant into a liquid phase when possible.

Use a scale to monitor the amount recovered.

Never use a recovery machine on a flammable refrigerant unless rated for it.

Follow EPA requirements for recovery and recycling.

Label recovery cylinders.

ASHRAE Standard 34 classifies refrigerants by toxicity and flammability.

A1 refrigerants have low toxicity and no flame propagation.

A2L refrigerants have low toxicity and lower flammability.

A3 refrigerants have low toxicity and high flammability.

B1 refrigerants have higher toxicity and no flame propagation.

B2 refrigerants have higher toxicity and lower flammability.

Always consult the SDS and ASHRAE 34.

The Montreal Protocol phases out ozone-depleting substances.

The Kigali Amendment phases down HFCs.

The EPA's AIM Act implements the HFC phase-down in the U.S.

R-22 production and import are phased out in the U.S.

R-404A has a high GWP and is being replaced by lower-GWP refrigerants.

Compliance requires recordkeeping and proper recovery and disposal.

Check current EPA regulations.

Electronic leak detectors are sensitive to small leaks.

Soap bubbles confirm a leak found with an electronic detector.

Ultraviolet dye can be added to the system to trace leaks.

Pressure testing with dry nitrogen can reveal leaks.

Ultrasonic leak detectors can detect leaks in noisy environments.

A system that will not hold vacuum has a leak or moisture.

Follow the manufacturer's instructions for the leak detection method.

Charge by weight when the nameplate charge is known.

Charge by superheat when the system has a fixed orifice.

Charge by subcooling when the system has a TEV and a receiver.

Never charge liquid refrigerant into the suction line of a running compressor.

Use a scale to monitor the charge.

Verify the charge with a sight glass and moisture indicator.

Record the final charge and system readings.

Use DOT-approved recovery cylinders.

Never fill above 80% by volume.

Evacuate recovery cylinders before use.

Label cylinders with the refrigerant type and date.

Store cylinders upright and secured.

Transport cylinders with valve caps installed.

Never mix refrigerants in a recovery cylinder.

Recycling removes oil, moisture, and particulates from refrigerant.

Reclamation restores refrigerant to ARI 700 purity.

Reclaimed refrigerant can be resold and used in another appliance.

Recovered refrigerant that is not recycled or reclaimed must be disposed of properly.

Never vent refrigerant to the atmosphere.

Keep records of refrigerant recovered, recycled, and reclaimed.

Follow EPA Section 608 requirements.

Wear gloves and eye protection when handling refrigerants.

Work in a well-ventilated area.

Do not allow refrigerant to contact open flames.

Use a refrigerant detector in enclosed spaces.

Follow the SDS for the specific refrigerant.

Store cylinders in a cool, dry, well-ventilated area.

Never use refrigerant to clean equipment or as a propellant.

The compressor raises the pressure and temperature of the refrigerant vapor.

The condenser rejects heat from the refrigerant.

The metering device reduces the pressure and temperature of the refrigerant.

The evaporator absorbs heat from the space.

The receiver stores liquid refrigerant.

The filter-drier removes moisture and particulate.

The sight glass indicates refrigerant charge and moisture content.

The thermostat controls the box temperature.

The low-pressure switch protects the compressor and controls pump-down.

The high-pressure switch protects the system from excessive discharge pressure.

The oil pressure safety switch protects the compressor from lubrication failure.

The defrost timer controls the defrost cycle.

The defrost termination switch ends the defrost cycle.

The fan delay switch delays the evaporator fans after defrost.

High head pressure: dirty condenser, non-condensable gases, overcharge, or high ambient.

Low head pressure: undercharge, low ambient, or a failed compressor.

High suction pressure: overcharge, high load, or a failed compressor valve.

Low suction pressure: undercharge, restriction, or a failed metering device.

High superheat: undercharge, restriction, or a stuck-closed TEV.

Low superheat: overcharge, overfed evaporator, or a stuck-open TEV.

High subcooling: overcharge or non-condensable gases.

Low subcooling: undercharge or a restriction.

Evacuate to 500 microns and hold for 10-15 minutes.

Use a micron gauge at the system.

Triple evacuation removes moisture and non-condensables.

Never use the system compressor to evacuate the system.

Replace the filter-drier before evacuation.

Check for leaks if the vacuum does not hold.

Charge the system only after a successful evacuation.

Use dry nitrogen for pressure testing.

Pressurize the system to the manufacturer's recommended test pressure.

Use an electronic leak detector or soap bubbles to locate leaks.

Repair leaks and retest before charging.

Replace the filter-drier after any repair that opens the system.

Evacuate the system after repair.

Document the leak test and repair.

Charge by weight when the nameplate charge is known.

Charge by superheat or subcooling when the nameplate charge is unknown.

Never charge liquid refrigerant into the suction line of a running compressor.

Use a scale to monitor the charge.

Verify the charge with a sight glass and moisture indicator.

Record the final charge and system readings.

Check for leaks after charging.

Verify the system is evacuated and charged.

Check the compressor oil level and rotation.

Verify the condenser and evaporator fan rotation.

Check the control settings.

Record initial pressures, temperatures, superheat, subcooling, and amp draw.

Verify the system pulls down to the design temperature.

Check for leaks and proper charge after the system stabilizes.

Clean condenser coils regularly.

Check and replace filter-driers when pressure drop exceeds 2-3 psi.

Verify defrost termination and fan delay settings.

Check door gaskets and closers.

Verify refrigerant charge by weight or by subcooling/superheat.

Check electrical connections for tightness.

Document refrigerant added, recovered, or recycled.

Cooler design temperature is typically 35-38 °F.

Freezer design temperature is typically 0 °F or lower.

Evaporator TD is typically 10 °F for coolers and 10-15 °F for freezers.

Condenser TD is typically 10-15 °F.

Suction lines should be sized for oil return and minimal pressure drop.

A P-trap at the base of a suction riser returns oil to the compressor.

The receiver must be sized to hold the entire system charge plus a 10-15% margin.

Lock out and tag out the power source before servicing.

Use a meter rated for the voltage and category.

Discharge capacitors before handling.

Verify the compressor is off before opening the terminal box.

Use insulated tools and PPE.

Check for proper grounding and bonding.

Follow NFPA 70E for electrical safety.

Manifold gauge set with correct hoses and gauges.

Digital thermometer or thermocouple for superheat and subcooling.

Vacuum gauge (micron gauge) for evacuation.

Refrigerant leak detector.

Clamp-on ammeter for compressor amp draw.

Multimeter for voltage, resistance, and continuity.

Refrigerant recovery machine and DOT-approved recovery cylinder.

High head pressure with high subcooling: dirty condenser, non-condensable gases, or overcharge.

High head pressure with low subcooling: undercharge or a restriction.

Low suction pressure with high superheat: undercharge, restricted liquid line, or stuck-closed TEV.

Low suction pressure with low superheat: overfed evaporator, stuck-open TEV, or failed compressor valve.

Compressor runs but does not cool: failed compressor valve, low charge, or restricted metering device.

Compressor trips on overload: high head pressure, low voltage, failed run capacitor, or seized compressor.

Ice on suction line: low charge or restricted TEV.

Charge by weight when the nameplate charge is known.

Charge by superheat when the nameplate charge is unknown and the system has a fixed orifice.

Charge by subcooling when the system has a TEV and a receiver.

Overcharging raises head pressure and subcooling.

Undercharging raises superheat and reduces capacity.

Verify the sight glass is clear after charging.

Record the final charge and system readings.

Reciprocating compressors use pistons and valves.

Scroll compressors use two intermeshing scrolls.

Screw compressors use two rotors.

Semi-hermetic compressors can be rebuilt.

Hermetic compressors are welded and typically replaced.

Compressor valve failure causes low capacity and high discharge temperature.

Low oil indicates oil return problems or a leak.

Air-cooled condensers reject heat to ambient air.

Water-cooled condensers use water or a cooling tower.

Evaporator coils should be cleaned regularly.

Evaporator fan motors should be checked for proper rotation.

The evaporator TD affects humidity.

Condenser subcooling circuits increase subcooling.

Coil fin damage reduces airflow and heat transfer.

Electric defrost uses heater elements in the evaporator.

Hot gas defrost uses hot discharge gas to melt frost.

Off-cycle defrost relies on the compressor stopping.

Defrost termination temperature is typically 45-55 °F for electric defrost.

Fan delay settings keep evaporator fans off until the coil is below about 35 °F.

A failed defrost heater, termination switch, or timer causes ice buildup.

Defrost frequency should match frost accumulation.

Evacuate to 500 microns and hold for 10-15 minutes.

Use a micron gauge at the system.

Triple evacuation removes moisture and non-condensables.

Leak detection methods include electronic detectors, soap bubbles, ultraviolet dye, and pressure testing with nitrogen.

Never use oxygen or air for pressure testing.

A system that will not hold vacuum has a leak or moisture.

Replace the filter-drier after repair.

Lock out and tag out the power source before servicing.

Use a meter rated for the voltage and category.

Discharge capacitors before handling.

Verify the compressor is off before opening the terminal box.

Use insulated tools and PPE.

Check for proper grounding and bonding.

Follow NFPA 70E for electrical safety.

A thermostat cycles the compressor or a solenoid valve.

A pressure control can be used for pump-down or low-ambient operation.

An electronic controller may control temperature, defrost, and alarms.

A solenoid valve controls refrigerant flow to the evaporator.

A hot gas bypass valve modulates capacity.

A time delay relay prevents short cycling.

Alarm systems should be tested regularly.

Suction lines should minimize pressure drop while maintaining oil return velocity.

Liquid lines should minimize pressure drop and prevent flashing.

Discharge lines should minimize pressure drop and maintain oil return.

Suction risers should be sized for oil return at minimum load.

Horizontal suction lines should slope toward the compressor.

Piping should be supported and insulated.

Brazing should use dry nitrogen purge.

Recovery equipment must be certified to ARI 740.

Use the correct recovery cylinder for the refrigerant type.

Recovery cylinders must be evacuated before use.

Never fill above 80% by volume.

Recovered refrigerant may be recycled or reclaimed.

Never mix refrigerants in a recovery cylinder.

Label recovery cylinders with the refrigerant type and date.

Verify the system is evacuated, charged, and all valves are in the correct position.

Check the compressor oil level and rotation.

Verify the condenser fan and evaporator fan rotation and amp draw.

Check the control settings.

Record initial pressures, temperatures, superheat, subcooling, and amp draw.

Verify the system pulls down to the design temperature.

Check for leaks and proper charge after the system stabilizes.