RAC Servicing (DomRAC) NC II flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Hierarchy of hazard control

Order of effectiveness from best to weakest: elimination, substitution, engineering controls, administrative controls, then personal protective equipment. PPE is the last line of defense, not the first choice.

Lockout/tagout sequence

Notify affected workers, shut down, isolate the energy source, apply lock and tag, release stored energy such as capacitors and pressure, then verify zero energy before starting work.

Fire classes A, B, C

Class A is ordinary combustibles extinguished with water; Class B is flammable liquids using foam, CO2, or dry chemical; Class C is energized electrical using CO2 or dry chemical, never water.

Manifold gauge color code

Blue hose connects to the low-pressure suction side, red to the high-pressure discharge side, and yellow to the center service port for vacuum, recovery, or charging operations.

Superheat formula

Superheat equals suction line temperature minus the evaporating saturation temperature at suction pressure. For fixed-orifice or capillary systems, a target of about 5 to 10 K is typical.

Micron and evacuation target

One micron equals 1/1000 mm Hg and atmospheric pressure is about 760,000 microns. A vacuum of 500 microns or lower held for 15 minutes with the pump isolated indicates acceptable dehydration.

Flare and torque rule

Flare faces must be square, burr-free, and lightly oiled, and flare nuts are tightened to the manufacturer's torque with a torque wrench rather than by feel to prevent leaks.

Nitrogen purge while brazing

Flow dry nitrogen at low pressure through the pipe during brazing to prevent internal oxidation scale, which can later block the capillary tube, strainer, or thermostatic expansion valve.

Pressure test with dry nitrogen

Pressurize the system with dry nitrogen to the manufacturer's test pressure, typically 1.5 times working pressure, and hold. A pressure drop corrected for temperature indicates a leak.

Triple evacuation procedure

Evacuate the system, break the vacuum with dry nitrogen, and repeat three times, finishing with a deep evacuation to 500 microns held for 15 minutes to confirm no moisture or leak.

Condensate trap purpose

On a draw-through coil, a trap equal to the coil static pressure prevents air from being pulled in through the drain, which would otherwise cause overflow and water damage.

Delta-T check

The indoor air temperature drop across a properly operating domestic split evaporator is typically 8 to 11 K. A low value suggests low charge, dirty coil, or low airflow.

Capacitor microfarad test

Measure the capacitor with a meter set to capacitance and compare to the rated microfarads, allowing about plus or minus 6 percent. A bulged or out-of-range capacitor is replaced.

Condenser cleaning direction

Wash coils from the clean side toward the dirty side so debris is pushed out rather than driven deeper into the fins, and rinse chemical cleaners fully to avoid corrosion.

Subcooling formula

Subcooling equals the condensing saturation temperature at discharge pressure minus the liquid line temperature. For thermostatic expansion valve systems, a target of about 5 to 10 K is typical.

Compressor winding tests

An open winding reads infinite resistance, a shorted winding reads near zero, and a grounded winding shows continuity to the shell. Compare windings to each other for balance.

Frozen evaporator causes

A frozen evaporator results from restricted airflow such as a dirty filter or blocked return, low refrigerant charge, or a faulty defrost or fan control. Superheat and pressures distinguish them.

High discharge pressure causes

High discharge pressure points to a dirty condenser, failed condenser fan, overcharge, non-condensables in the system, or high ambient temperature. Check each in that order.

Restriction versus undercharge

Both cause low suction and high superheat. A restriction shows a temperature drop across the device such as the capillary or strainer, while undercharge shows low subcooling and no such drop.

Recovery cylinder fill limit

Never fill a recovery cylinder above 80 percent of its water capacity by weight. Use a scale, keep the cylinder upright, and never heat it with an open flame.

Recovery versus recycling

Recovery removes refrigerant from a system. Recycling cleans it on site of oil, moisture, and particulates but does not restore AHRI 700 purity; reclamation does that at a certified facility.

Refrigerant vapor density hazard

Refrigerant vapor is heavier than air and collects at floor level in basements and plant rooms, displacing oxygen. Ventilate and test the atmosphere before entry.

Ozone depletion potential

ODP ranks a substance's ozone-destroying effect relative to CFC-11, which equals 1.0. CFCs are highest, HCFCs such as R-22 are about 0.055, and HFCs are zero.

Global warming potential

GWP ranks a substance's climate impact relative to carbon dioxide, which equals 1. R-410A is about 2,088, R-134a about 1,430, R-32 about 675, and propane about 3.

Venting prohibition

Deliberate release of refrigerant to the atmosphere during service, recovery, or disposal is prohibited. Refrigerant must be recovered, recycled, or reclaimed instead.

Zeotropic blend charging

Zeotropic blends such as R-407C have a temperature glide and must be charged as liquid from the cylinder to maintain the correct composition. R-410A has negligible glide.

Recovery methods compared

Liquid recovery is fastest, vapor recovery handles the final portion, and push-pull uses the system to move liquid into the cylinder. Small critically charged systems use vapor recovery only.

Refrigerant PPE

Wear safety glasses or goggles, refrigerant-rated gloves, long sleeves, and safety shoes. Liquid refrigerant causes frostbite, and vapor can displace oxygen in enclosed spaces.

Capacitor stored charge hazard

Capacitors hold charge after power is removed. Isolate and lock out the unit, then discharge the capacitor and verify with a meter before touching electrical terminals.

Refrigerant recordkeeping

Log the refrigerant type, amount recovered, amount charged, and cylinder identification for each job, and retain records for the period required by local regulation.

Leak repair obligation

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.