RAC Servicing (DomRAC) NC II cheat sheet

Communication is a two-way loop: sender encodes, receiver decodes and confirms via feedback; a job instruction is not complete until the receiver restates it ("close the loop").

5S workplace order: Sort (Seiri), Set in order (Seiton), Shine (Seiso), Standardize (Seiketsu), Sustain (Shitsuke) - the first three are physical, the last two are discipline.

Hierarchy of hazard control, best to weakest: elimination, substitution, engineering controls, administrative controls, PPE. PPE is the last line of defense, never the first.

Fire classes and media: Class A ordinary combustibles (water), Class B flammable liquids (foam, CO2, dry chemical), Class C energized electrical (CO2, dry chemical - never water).

Refrigerant cylinders and oxygen/acetylene sets are secured upright; oxygen and fuel gas stored at least 6 m apart or separated by a 30-minute fire-rated barrier.

Lockout/tagout sequence: notify, shut down, isolate, apply lock and tag, release stored energy (capacitors, spring pressure, refrigerant), verify zero energy, then work.

Quality record rule: if it is not documented, it is not done - work orders, torque/leak-test readings, recovered refrigerant weight, and customer sign-off are the evidence trail.

Confined-space and elevated work: any space with limited entry/exit and poor ventilation requires atmospheric testing and an attendant; fall protection is required at heights of 1.8 m or more.

Manifold gauge color code: blue = low side (suction), red = high side (discharge), yellow = center/service port to vacuum pump, recovery unit, or charging cylinder.

Pressure–temperature relation: at a given pressure a pure refrigerant boils/condenses at one fixed temperature; a measured saturation temperature lower than the pipe temperature indicates subcooling (liquid line), higher indicates superheat (suction line).

Superheat = suction line temperature minus evaporating (saturation) temperature at suction pressure; target 5–10 K for a fixed-orifice/ capillary system. Subcooling = condensing temperature minus liquid line temperature; target 5–10 K for TXV systems.

Micron scale: 1 micron = 1/1000 mm Hg. Atmospheric pressure ≈ 760,000 microns; a vacuum of 500 microns or below held for 15 minutes with the pump isolated indicates an acceptable dehydration.

Torque and flare rules: flare nuts are tightened to manufacturer torque with a torque wrench, not by feel; flare faces must be square, burr-free, and lubricated with a drop of refrigerant oil.

Tool care: torque wrenches stored at their lowest setting, micrometers and vernier calipers zeroed before use, gauge manifolds purged with the working refrigerant before connection to avoid cross-contamination.

Material compatibility: copper to copper brazed with silfos (no flux); copper to steel brazed with silver-bearing rod and flux; never braze on a pressurized or sealed system without a nitrogen purge.

Documentation set for a domestic unit: job order, equipment nameplate data (model, serial, refrigerant type and charge), pressure/temperature readings, leak-test result, and customer acknowledgment.

Nameplate first: record refrigerant type, factory charge in grams, voltage, and rated current before any piping decision; charge and pipe sizing follow the nameplate, not habit.

Line sizing and length: keep interconnecting piping as short and as few bends as possible; excessive length or vertical rise reduces capacity and requires added refrigerant per the manufacturer's per-meter allowance.

Brazing with nitrogen: flow dry nitrogen at low pressure through the pipe while brazing to prevent internal oxidation (scale), which later blocks the capillary tube, strainer, or TXV.

Pressure test: pressurize with dry nitrogen (typically to the manufacturer's test pressure, often 1.5× working pressure) and hold; a drop with temperature correction indicates a leak. Never use oxygen or refrigerant as a test gas for strength testing.

Evacuation: triple evacuation (break each vacuum with dry nitrogen) or a single deep evacuation to 500 microns held 15 minutes; decay of vacuum after isolation means moisture or a leak remains.

Electrical: verify supply voltage within ±10% of nameplate, correct breaker and wire gauge, grounding continuity, and that the outdoor unit has a dedicated circuit; polarity reversal on inverter units causes communication faults.

Commissioning checks: record ambient and indoor wet-bulb, suction and discharge pressures, superheat/subcooling, running amps versus nameplate RLA, condensate drain slope and trap, and airflow (static pressure or delta-T).

Condensate drainage: drain line slopes continuously downward, is insulated in humid spaces, and on draw-through coils includes a trap equal to the coil static pressure to prevent air pull-in and overflow.

Preventive maintenance intervals: clean or replace filters monthly to quarterly depending on dust load; clean condenser coil and check refrigerant charge and electrical connections at least annually.

Cleaning rule: condenser and evaporator coils are washed from the clean side toward the dirty side; fins are combed straight, never flattened; chemical coil cleaners are rinsed fully to avoid corrosion.

Delta-T check: a properly operating domestic split unit typically shows an indoor air temperature drop of 8–11 K across the evaporator; a low delta-T suggests low charge, dirty coil, or low airflow.

Electrical checks: measure capacitor microfarads against rating (±6%), check contactor pitting, compressor winding resistance balance, and insulation resistance to ground (megger) before condemning a compressor.

Lubrication and belts: only sealed bearings are used on most domestic fan motors; where a belt exists, tension is set to the manufacturer's deflection spec and pulleys are aligned with a straightedge.

Refrigerant charge verification: use superheat (fixed orifice) or subcooling (TXV) at steady-state conditions, not sight-glass bubbles alone; a clear sight glass only means no flash gas at that point.

Service documentation: record before/after readings (pressures, temperatures, amps, capacitor values) so the repair can be verified and the customer can see the change.

Diagnostic order: symptom → confirm with measurement → isolate to electrical, airflow, or refrigerant circuit → repair → verify. Never add refrigerant before confirming the actual fault.

Unit does not start: check supply voltage, breaker/fuse, thermostat call, door/float switch, control board error code, then compressor overload and start components.

Compressor hums and trips: suspect a failed run/start capacitor, seized compressor, or low voltage; verify capacitor microfarads and supply voltage before replacing the compressor.

Frozen evaporator: causes are restricted airflow (filter, blower, blocked return), low charge, or a faulty defrost/fan control; low charge and airflow restriction are distinguished by superheat and pressure readings.

High discharge pressure: dirty condenser, condenser fan failure, overcharge, non-condensables in the system, or high ambient; high suction with normal discharge points to an overcharge or inefficient compressor.

Low suction pressure with high superheat: undercharge, restriction (capillary, strainer, TXV), or a starved evaporator; a restriction shows a temperature drop across the device.

Electrical faults: open winding = infinite resistance, shorted winding = near zero resistance, grounded winding = continuity to the shell; compare each reading to the others for balance.

Ozone depletion potential (ODP) and global warming potential (GWP) rank refrigerants: CFCs highest ODP, HCFCs intermediate, HFCs zero ODP but high GWP; HFOs and natural refrigerants (CO2, ammonia, hydrocarbons) are low-GWP alternatives.

Recovery is mandatory before opening a circuit: recover into a dedicated recovery cylinder, never vent; the cylinder must be DOT/ISO-rated, in test date, and never filled above 80% of its water capacity.

Recovery cylinder safety: use a scale to control fill, weigh the cylinder before and after, keep it upright and below its pressure rating, and never heat a cylinder with an open flame.

Recovery machine setup: liquid recovery is faster than vapor; pull a vacuum on the recovery cylinder and hoses before use; use a filter-drier on the recovery line to remove moisture and acid.

Refrigerant safety: refrigerant vapor is heavier than air and displaces oxygen in low areas; a leak in a small room requires ventilation before entry; frostbite risk from liquid contact requires gloves and eye protection.

Leak detection: electronic leak detector, soap bubbles, or UV dye; nitrogen pressure testing is preferred for strength testing; never use a flame (halide torch) in a confined space.

Recordkeeping: log the refrigerant type, amount recovered, amount charged, and cylinder ID; recovered refrigerant is either recycled on site to the same owner's equipment or sent for reclamation.

Cylinder handling: keep valves closed and capped when not in use, store away from heat and direct sun, transport secured upright, and never drop or roll a cylinder on its side.

Ozone layer protection: CFCs and HCFCs release chlorine that destroys stratospheric ozone; the Montreal Protocol phases these out, and HFCs are controlled under the Kigali Amendment for their GWP.

Venting prohibition: deliberate release of refrigerant to the atmosphere during service, recovery, or disposal is prohibited; recovery, recycling, or reclamation is required.

Recovery efficiency targets: manufacturers specify recovery levels (commonly 90% of the charge for small units, or 80% under certain conditions); follow the equipment's rated recovery efficiency.

Decommissioning: before scrapping a unit, recover the full charge, remove and label the compressor oil, and dispose of components through licensed channels; never cut lines on a charged system.

Refrigerant labeling: cylinders and equipment must be labeled with the refrigerant type, and recovered refrigerant must be identified as recovered, not virgin.

Spill/leak response: evacuate and ventilate, stop the source if safe, remove ignition sources for flammable refrigerants, and report larger releases per local regulation.

Personal exposure: monitor oxygen in enclosed plant rooms; refrigerant concentrations that displace oxygen cause asphyxiation before odor is a reliable warning.

PPE for refrigerant work: safety glasses or goggles, refrigerant-rated gloves, long sleeves, and safety shoes; add a respirator only per SDS requirements for specific refrigerants.

Cylinder pressure rises with temperature: a cylinder left in the sun or near a heat source can exceed its relief device setting; store below the temperature stamped on the cylinder.

Never mix refrigerants in a recovery cylinder: mixed refrigerant cannot be reclaimed economically and must be destroyed; label each cylinder with the single refrigerant type it holds.

Hose and manifold safety: inspect hoses for cracks and bulges, never exceed the working pressure rating, and never use a hose as a structural support or handle.

Brazing safety: purge nitrogen only at low flow (a regulator, not full cylinder pressure), keep a fire extinguisher within reach, and never braze near refrigerant vapor or oil residue.

Electrical safety during service: isolate and lock out the unit before opening the electrical box; capacitors hold charge after power-off - discharge and verify with a meter.

Ventilation first: before entering a plant room or basement with a suspected leak, ventilate and test the atmosphere; refrigerant is heavier than air and collects at floor level.

Recovery methods: liquid recovery (push-pull or liquid line) is fastest; vapor recovery is used for the final portion; a combined method recovers most of the charge as liquid, then finishes as vapor.

Push-pull recovery: uses the system compressor or a recovery unit to push liquid into the cylinder and pull vapor back; requires the correct valve alignment and is not used on small critically charged systems.

Recovery cylinder fill limit: never exceed 80% of the cylinder's water capacity by weight; use a scale and stop when the calculated weight is reached.

Vacuum and dehydration: after recovery and repair, evacuate to 500 microns and hold; a rising vacuum indicates moisture or a leak, requiring further dehydration or leak repair.

Recycling versus reclamation: recycling removes oil, moisture, and particulates on site but does not restore the refrigerant to AHRI 700 purity; reclamation does, and requires a certified facility.

Recovery unit maintenance: change the filter-drier and oil when the unit's efficiency drops, and never operate a recovery unit without the correct inlet filter to protect the compressor.

Cylinder identification: use the cylinder color code and label for the refrigerant; never fill an unlabeled or mismatched cylinder, and keep the valve cap on during transport.

Technician certification: refrigerant handling typically requires a nationally recognized certification (for example, an EPA Section 608-type credential in the US); verify the local requirement before servicing.

Record retention: service records for refrigerant recovered, charged, and leak repairs are kept for the period required by local regulation and made available on request.

Leak repair obligations: appliances above a threshold charge must be repaired within a set period after a leak is detected, or the owner must document a retrofit or retirement plan.

Refrigerant sales restrictions: sale of refrigerant to uncertified persons is restricted in many jurisdictions; purchase and resale require proof of certification.

Disposal documentation: when a unit is scrapped, the refrigerant must be recovered before disposal and the recovery documented; the scrap dealer must not accept a charged appliance.

Labeling requirements: equipment must show the refrigerant type and charge; after a retrofit, a new label stating the refrigerant and the oil type is required.

Regulatory hierarchy: international treaty (Montreal/Kigali) → national law → local permit and licensing rules; the strictest applicable requirement governs the job.

GWP is expressed relative to CO2 = 1; R-410A ≈ 2,088, R-134a ≈ 1,430, R-32 ≈ 675, R-290 (propane) ≈ 3, CO2 = 1. Higher GWP means a larger climate impact per kilogram released.

ODP is relative to CFC-11 = 1.0; HFCs have ODP = 0 but are still greenhouse gases; HCFCs such as R-22 have small but nonzero ODP (≈0.055).

Refrigerant blends: zeotropic blends (e.g., R-407C) have a temperature glide and must be charged as liquid; near-azeotropic blends (R-410A) have negligible glide.

Flammable refrigerants (A2L/A3): R-32 and R-290 require reduced charge limits, no ignition sources in the work area, and leak detection per the applicable safety standard.

Energy efficiency: correct charge, clean coils, and correct airflow reduce indirect emissions, which often exceed the direct refrigerant emissions over a unit's life.

Recovery versus destruction: recovered refrigerant that cannot be reclaimed must be destroyed at a licensed facility; never release it to the atmosphere.

Leak prevention: brazed joints, torque-checked flares, and pressure testing before charging reduce refrigerant loss and the associated environmental impact.