RAC Servicing (DomRAC) NC II key terms

The number of degrees a refrigerant vapor is above its saturation temperature at a given pressure. Measured at the evaporator outlet, it confirms the expansion device is feeding the coil correctly and that no liquid reaches the compressor.

The number of degrees a liquid refrigerant is below its saturation temperature at a given pressure. Measured at the condenser outlet, it shows how much liquid is stacked in the condenser and helps verify correct charge.

The temperature at which a refrigerant changes between liquid and vapor at a given pressure. On a pressure-temperature chart it converts a gauge reading into the corresponding boiling or condensing temperature used for superheat and subcooling calculations.

A reference table listing the saturation pressure of a refrigerant at each temperature. Technicians use it to translate gauge readings into temperatures and to compare expected versus actual system performance for the refrigerant in use.

A service tool with two gauges and valves that connects to the low and high sides of a system. It reads operating pressures and provides ports for evacuation, charging, and recovery without cross-contaminating the circuits.

A compressor-driven device that pulls refrigerant vapor and liquid from a system into a recovery cylinder instead of venting it to the atmosphere. It is required by environmental regulations whenever a system is opened or decommissioned.

A refillable, DOT- or locally approved pressure vessel used only for recovered refrigerant. It must never be filled above its marked capacity, must be labeled with the refrigerant type, and must be evacuated before first use.

Deliberately releasing refrigerant gas into the atmosphere. It is prohibited for most refrigerants because of ozone depletion and global warming potential; recovery, recycling, or reclaiming is required instead.

A relative number describing how strongly a substance destroys stratospheric ozone compared with CFC-11, which is set at 1.0. It guides the choice of refrigerant and the handling rules that apply to it.

A relative number describing how much heat a gas traps in the atmosphere over a set period compared with carbon dioxide, set at 1.0. It drives refrigerant selection, leak prevention, and recovery obligations.

A refrigerant family containing chlorine, fluorine, and carbon, such as R-12. These substances have high ozone depletion potential and are phased out; they must be recovered and never released during service.

A refrigerant family such as R-22 that contains chlorine and therefore still depletes ozone, though less than CFCs. Its production and use are restricted under phase-out schedules, so recovered amounts must be handled and recorded properly.

A refrigerant family such as R-410A and R-134a that contains no chlorine, so it does not deplete ozone, but it has significant global warming potential and must still be recovered rather than vented.

A refrigerant mixture whose components boil at different temperatures, so it changes temperature as it evaporates or condenses. It must be charged as a liquid and its leaks are harder to top up accurately.

A refrigerant mixture that behaves like a single substance, boiling and condensing at one constant temperature at a given pressure. It can be charged as vapor without changing its composition.

The temperature difference between the bubble point and dew point of a zeotropic refrigerant during phase change. It affects how superheat and subcooling are read and requires care when charging or checking a system.

The process of finding escaping refrigerant using electronic detectors, soap bubbles, ultraviolet dye, or pressure testing. Early detection protects the environment, saves charge, and prevents compressor damage from low suction pressure.

Pulling a system down to a deep vacuum with a pump to remove air and moisture before charging. It is confirmed with a micron gauge and prevents ice blockage, acid formation, and reduced capacity.

A pump that removes air and water vapor from a sealed system so it can be charged with refrigerant. It must use fresh oil and be connected through proper hoses and a valve to reach the required vacuum level.

An electronic instrument that measures deep vacuum in microns of mercury. It verifies that evacuation has removed moisture and non-condensables, which ordinary manifold gauges cannot show accurately.

The amount of refrigerant a system contains. It is set by weighing in the nameplate value or adjusted by superheat or subcooling readings, and an incorrect charge causes poor cooling and compressor stress.

A metering device that controls refrigerant flow into the evaporator by sensing outlet temperature and pressure. It maintains a set superheat so the coil is fully used without flooding the compressor.

A narrow fixed-bore tube that meters refrigerant into the evaporator and equalizes pressure when the compressor stops. It is inexpensive but cannot adjust to changing loads, so charge accuracy is critical.

The heat exchanger where liquid refrigerant absorbs heat from the refrigerated space or air and boils into vapor. Its airflow, cleanliness, and frost condition directly affect cooling capacity and superheat.

The heat exchanger where hot compressed refrigerant vapor releases heat to the surroundings and condenses into liquid. Dirty coils or poor airflow raise condensing pressure and reduce system efficiency.

The pump that raises refrigerant pressure and moves it around the circuit. It must never draw liquid refrigerant, so superheat, lubrication, and correct charge are essential to its life.

The movement of air across the evaporator and condenser, measured in volume per unit time. Restricted airflow from dirty filters, blocked coils, or wrong fan speed causes low capacity and high pressures.

The resistance a fan must overcome to move air through ducts, filters, and coils. Measuring it helps diagnose low airflow and confirm that the blower is delivering the design volume.

An instrument that measures air velocity at grilles, registers, or duct openings. Combined with duct area, it gives the air volume needed to check airflow against design values.

A safety device that opens the compressor circuit when current or temperature exceeds safe limits. Repeated tripping points to high head pressure, low voltage, or a failing compressor rather than a faulty protector.

The current a motor draws when its rotor cannot turn, typically several times running current. It is used to size protection and to judge whether a compressor is seized or receiving inadequate voltage.

A component that stores electrical energy to start or run a motor. A weak or bulged capacitor causes hard starting, overheating, and low torque, and is checked by measuring microfarads.

A test instrument that measures voltage, resistance, and current. It is used to check power supply, windings, switches, and continuity before and after replacing electrical parts.

An instrument that measures current by surrounding a conductor with a jaw, without breaking the circuit. It is used to read compressor and fan running amps and compare them with nameplate values.

A safety procedure that isolates energy sources and attaches a lock and warning tag before service. It prevents accidental startup or release of stored energy while a technician works on equipment.

Wearable gear such as gloves, goggles, and safety shoes that shields a technician from cold burns, refrigerant spray, and electrical hazards. It must be inspected, fit properly, and be used as required.

A structured review of a task to identify what could cause harm and how to control it. It is done before work begins and covers electrical, pressure, chemical, and fall risks.

A written authorization describing the job, equipment, reported fault, and required completion details. It links the technician's findings and parts used to the customer record and maintenance history.

The document a technician completes after a job, recording symptoms, tests, actions taken, parts replaced, and final readings. It supports warranty claims, billing, and future troubleshooting.

A structured list of checks performed when a unit is first installed, covering electrical connections, pressure test, evacuation, charge, airflow, and temperature drop. Sign-off confirms the system meets design and safety requirements.