Red Seal Refrigeration & AC Mechanic cheat sheet

Ozone Depletion Potential (ODP) is referenced to CFC-11 = 1.0; Global Warming Potential (GWP) is referenced to CO2 = 1 over 100 years (CO2 itself = 1, R-410A ≈ 2088, R-134a = 1430).

Under the Montreal Protocol phase-out schedule, HCFCs such as R-22 are being eliminated; HFCs are controlled under the Kigali Amendment.

Refrigerant cylinders must be hydrostatically tested every 5 years in Canada and are never filled above 80% of capacity by liquid volume (leave vapour space for expansion).

A refrigerant leak in a confined space displaces oxygen; R-22 and other halocarbons are heavier than air and collect at low points, so ventilate and test the atmosphere before entry.

A confined-space entry requires atmospheric testing for O2 (19.5–23%), flammability (below 10% LEL) and toxicity before entry, plus a standby attendant and rescue plan.

Exposure limits: R-22 and R-134a have occupational exposure limits around 1000 ppm (8-hour TWA); R-410A is also about 1000 ppm. Never use odour as a leak indicator.

Recovery cylinders must be DOT/TC-approved, clearly labelled with the refrigerant type, and never mixed; mixed refrigerants must be destroyed or reclaimed, not reused.

Personal protective equipment for brazing includes welding goggles, gloves and adequate ventilation; phosgene gas can form if refrigerant contacts an open flame.

A manifold gauge set reads low-side (compound, blue) and high-side (red) pressures; the centre port (yellow) connects to the recovery/vacuum pump or charging cylinder.

A micron gauge measures absolute pressure in microns; 1 atmosphere ≈ 760,000 microns, and a good vacuum target for a tight system is below 500 microns.

A vacuum decay (standing vacuum) test: pull below 500 microns, isolate the pump, and confirm the rise stays under about 500 microns in 10 minutes.

A digital electronic leak detector is more sensitive than soap bubbles; use it at joints, valves and the evaporator coil, and confirm with soap solution.

A clamp-on ammeter measures current without breaking the circuit; use a voltmeter in parallel and an ohmmeter only on a de-energized circuit.

A superheat/subcool calculator or a thermometer with a clamp probe is used to set the charge; a psychrometer measures wet- and dry-bulb for airflow and load checks.

Torque wrenches and flaring/ swaging tools are used for flare and press fittings; a tubing cutter leaves burrs that must be reamed to avoid restriction and contamination.

Nitrogen flow while brazing prevents internal oxidation (scale); a nitrogen regulator and flow meter are required for a proper purge.

The refrigeration cycle: compression (low-pressure vapour to high-pressure vapour), condensation (reject heat, become liquid), expansion (pressure drop), evaporation (absorb heat, become vapour).

Sensible heat changes temperature; latent heat changes state at constant temperature. Latent heat of vaporization of water is about 970 Btu/lb (2260 kJ/kg) at 100°C.

1 ton of refrigeration = 12,000 Btu/h = 200 Btu/min = 3.517 kW = 3024 kcal/h.

Superheat = actual suction temperature minus evaporating (saturated suction) temperature; subcooling = condensing temperature minus liquid line temperature.

Carnot/COP: COP = refrigeration effect / work input; a higher evaporating temperature and lower condensing temperature both raise capacity and efficiency.

Pressure–enthalpy (P-h) diagram: the compressor raises pressure and enthalpy; the expansion device is isenthalpic (constant enthalpy) in the ideal cycle.

Psychrometrics: relative humidity = actual vapour pressure / saturation vapour pressure at the same dry-bulb; dew point is the temperature at which air reaches saturation.

Heat transfer: conduction Q = kAΔT/L; convection Q = hAΔT; radiation Q = εσA(T1⁴ − T2⁴). Total heat = sensible + latent.

Ohm's law: V = IR; power P = VI = I²R. Single-phase power = V × I × PF; three-phase power = √3 × V × I × PF.

Motor capacitor-start circuits use a start capacitor and centrifugal switch; a run capacitor improves power factor and torque on permanent split capacitor (PSC) motors.

A potential relay drops out the start capacitor when the motor's back-EMF (voltage across the start winding) rises; a current relay drops out when current falls.

Motor winding checks: resistance between windings and to ground (megohmmeter, >1 MΩ acceptable) and a balance check on three-phase windings (within a small tolerance).

Thermostatic expansion valve and pressure controls use a low-voltage control circuit; a step-down transformer (e.g., 240/24 V) supplies it.

A contactor coil is energized by the control circuit; the contacts carry the compressor/condenser load. Check coil voltage and contact pitting before replacing.

Defrost controls: time-initiated, temperature- or pressure-terminated; a defrost timer and termination thermostat/klixon work together.

Solid-state controls: a thermistor changes resistance with temperature; a transducer converts pressure to a voltage/current signal for the controller.

Copper tubing is sized by outside diameter (OD) in North America; ACR tubing is cleaned and capped for refrigeration service.

Brazing uses filler (silver/phosphorus alloys) above 450°C; soldering uses tin-lead or lead-free alloys below 450°C and is not acceptable for high-pressure refrigerant lines.

Use a nitrogen purge during brazing; use flux only on the outside of the joint and clean it off after brazing to prevent corrosion.

Suction lines are insulated and sloped back to the compressor; liquid lines are not insulated unless exposed to heat gain; hot-gas lines are arranged to avoid oil trapping.

Oil return: use traps (P-traps) at the base of risers and ensure velocity in vertical suction risers is adequate to carry oil back to the compressor.

Line sizing balances pressure drop (typically ≤2°F equivalent in the suction line) against oil return; undersized lines cause capacity loss, oversized lines cause oil logging.

Filter driers are installed in the liquid line (or suction line for burnout cleanup); install with flow arrow correct and replace after any major repair.

A sight glass with moisture indicator shows liquid line full of liquid and indicates moisture; bubbles suggest flash gas or undercharge.

Refrigerant classes: CFCs (R-12), HCFCs (R-22), HFCs (R-134a, R-410A), HFOs (R-1234yf). R-410A is a near-azeotropic blend of R-32/R-125 (50/50) and must be charged as a liquid.

Mineral oil is used with CFCs and HCFCs; POE (polyol ester) is used with HFCs and HFOs; PAG is used in automotive systems. POE is hygroscopic-keep containers sealed.

Recovery removes refrigerant from a system; recycling cleans it on site (oil separation, filter); reclamation returns it to AHRI 700 purity specification and requires an EPA-certified reclaimer.

Never vent refrigerant; recover to the required vacuum level (typically 500 microns or per local regulation) before opening the system.

Liquid charging requires the cylinder inverted or a liquid-charging valve; vapour charging is slow and used only for small amounts on the low side.

Refrigerant blends may fractionate on leakage; a significant leak means recover, evacuate and recharge by weight, not top-up.

A refrigerant identifier is used to verify the gas before recovery to avoid mixing; a moisture indicator and acid test confirm oil and system condition.

Oil pressure safety switches and proper oil level (sight glass on the crankcase) protect the compressor; low oil pressure trips the compressor to prevent damage.

Evacuation: pull a deep vacuum (below 500 microns) and perform a standing vacuum test; a triple evacuation with nitrogen breaks is used on wet systems.

Weigh in the charge by weight whenever possible; use superheat (fixed orifice/TXV) or subcooling (TXV with receiver) to verify the final charge.

Record baseline data at start-up: ambient and space temperatures, suction and discharge pressures, superheat, subcooling, amp draw, and static pressures.

Check rotation on three-phase compressors and fans; reverse rotation causes high current, low capacity and possible compressor damage.

Confirm all electrical connections are tight, overloads are set to nameplate amps, and safety controls (high/low pressure, oil failure, freeze stat) are functional.

Verify airflow at start-up: measure external static pressure and compare to the fan curve; check filter, belt tension and pulley alignment.

Leak test with nitrogen and a trace of refrigerant (or dry nitrogen pressure test) before evacuation; never pressurize with oxygen or air.

Document and tag the system with refrigerant type, charge weight, and service history; leave the site clean and all panels secured.

High superheat + low suction pressure = undercharge, restriction, or starving evaporator; low superheat + flooding = overcharge or excessive airflow/valve problem.

High discharge pressure causes: dirty condenser, high ambient, non-condensables, overcharge, or restricted condenser airflow.

Low suction pressure causes: restricted liquid line/filter drier, undercharge, faulty TXV, iced evaporator, or low load.

Compressor short-cycling: check high/low pressure controls, overloads, thermostat, and control circuit; a tripped internal overload indicates overheating or high current.

Amp draw above nameplate indicates mechanical drag, high head pressure, low voltage, or bad run capacitor; below nameplate can indicate low load or valve problem.

Ice on the suction line or evaporator signals low refrigerant, restriction, or airflow problem; find the cause, not just defrost it.

Planned maintenance: clean coils and drains, check belt tension and bearings, verify refrigerant charge, tighten electrical terminations, and test safeties.

Use a systematic approach: gather symptoms, verify with gauges and meters, isolate the fault, repair, then re-verify superheat/subcool and amp draw.

System types: direct expansion (DX), flooded, and liquid overfeed; commercial systems include self-contained, remote, and rack/parallel systems.

Compressor types: reciprocating, scroll, screw, and centrifugal; each has specific capacity ranges and maintenance needs.

Condensers: air-cooled, water-cooled (shell-and-tube), and evaporative; head pressure controls maintain adequate pressure at low ambient.

Evaporators: forced-air, gravity, and plate/finned coils; defrost methods include air, electric, hot gas, and water.

Controls: low-pressure pump-down, thermostat, defrost timer, EPR (evaporator pressure regulator), and CPR (crankcase pressure regulator).

A receiver stores liquid refrigerant; a liquid line solenoid valve with pump-down control prevents liquid migration to the compressor.

Industrial systems use ammonia (R-717) or CO2; ammonia is toxic and flammable at high concentrations, requiring detection and ventilation.

Refrigeration racks use parallel compressors and a common condenser; oil management and equalization are critical on multi-compressor racks.

Airflow: CFM = (sensible heat Btu/h) / (1.08 × ΔT °F); total heat = 4.5 × CFM × Δh (Btu/lb).

Sensible heat ratio (SHR) = sensible heat / total heat; equipment must be selected so its SHR matches the load.

Duct sizing: use the equal-friction method or velocity method; friction loss charts give pressure drop per 100 ft for a given CFM and duct size.

Static pressure: total external static pressure is measured across the blower; compare to the fan performance curve to determine actual CFM.

A psychrometric chart plots dry-bulb, wet-bulb, dew point, humidity ratio, enthalpy, and specific volume; use it to find apparatus dew point and coil bypass factor.

Heating: fossil-fuel furnaces and electric resistance; check gas pressure, combustion air, flue draft, and heat exchanger integrity.

Ventilation: outdoor air requirements per ASHRAE 62.1; balance exhaust and supply to maintain building pressure.

Filters are rated by MERV; higher MERV means finer filtration but higher pressure drop-verify blower capacity before upgrading.