NVQ L4 Automobile AC Technician key terms

Legislation controlling fluorinated greenhouse gases, requiring certified handling, leak checks, recovery of refrigerant and record keeping. It sets global warming potential limits and bans venting to atmosphere.

A number expressing how much heat one kilogram of a gas traps over 100 years compared with carbon dioxide. Used to compare refrigerants and to calculate CO2-equivalent charge sizes for regulations.

The mass of refrigerant in a system multiplied by its global warming potential, expressed in tonnes of CO2 equivalent. It determines which leak-check intervals and record duties apply.

A document supplied with a chemical listing its hazards, first-aid measures, handling and storage advice and disposal requirements. It must be available where refrigerants and oils are stored or used.

Wearable protection such as safety glasses, cryogenic gloves and face shield used when handling refrigerants and oils. It guards against frostbite, eye splash and skin contact during recovery and charging.

Tissue damage caused when liquid refrigerant contacts skin and boils off rapidly, freezing tissue. Affected areas must not be rubbed; flush with lukewarm water and seek medical help.

The danger that heavier-than-air refrigerant vapour displaces oxygen in pits, service bays or vehicle interiors. Work areas need ventilation and never-smell-testing rules; entry into confined spaces requires assessment.

Deliberately releasing refrigerant to atmosphere, which is prohibited in most jurisdictions. Recovered refrigerant must instead be collected in a suitable cylinder for recycling, reclamation or destruction.

The process of removing refrigerant from a system and storing it in an external cylinder without testing or cleaning it. Recovery is the first stage before recycling, reclamation or disposal.

Reducing contaminants in recovered refrigerant by oil separation and filtration so it can be reused, typically in the same vehicle. It does not achieve the purity of reclamation and requires dedicated equipment.

Reprocessing recovered refrigerant to new-product specification by an approved facility, including chemical analysis and certification. Reclaimed refrigerant is supplied with documentation of purity and composition.

A refillable vessel rated and marked for recovered refrigerant, never filled above its stated capacity and never mixed with unknown gases. It carries a tare weight and a maximum fill limit, often 80 percent.

The empty weight of a refrigerant cylinder, stamped on the neck or shoulder. Gross weight minus tare weight gives the refrigerant content, which must not exceed the permitted fill.

The maximum mass of refrigerant a cylinder may hold, set to leave vapour space for expansion. Overfilling risks hydraulic pressure rise, valve damage and cylinder rupture when warmed.

Air or nitrogen trapped in a system or cylinder that does not liquefy at normal condenser conditions. It raises discharge pressure, reduces cooling and must be purged from recovery equipment or eliminated by correct evacuation.

A structured process of gathering symptoms, comparing measured pressures and temperatures with specifications and isolating the faulty component before repair. It relies on logical testing rather than parts substitution.

The fixed link between a refrigerant's saturation pressure and temperature, shown on a PT chart. Comparing measured pressure with expected temperature reveals undercharge, restriction or condenser problems.

The temperature of refrigerant vapour above its saturation temperature at the same pressure. Measured at the evaporator outlet, it confirms the evaporator is fully boiled and the charge is adequate.

The temperature of liquid refrigerant below its saturation temperature at the same pressure. Measured at the condenser outlet, it indicates liquid seal and charge level in the high side.

Finding the point where refrigerant escapes using electronic detectors, UV dye, soap solution or pressure testing with dry nitrogen. It must precede evacuation and charging to avoid repeat failure.

An instrument that senses refrigerant concentration in air and alarms near a leak. It must be calibrated, used with the correct refrigerant setting and checked against a known reference before testing.

A method where fluorescent dye is added to the system and leaks glow under ultraviolet light. It locates slow leaks but requires cleaning of residue and correct dye compatibility.

A metering device that throttles liquid refrigerant into the evaporator and regulates flow to maintain superheat. A sticking or incorrectly set valve causes poor cooling or evaporator icing.

A fixed restriction that meters refrigerant flow in many mobile systems, often with a filter screen. It cannot adjust, so charge level and condenser performance strongly affect cooling.

The heat exchanger that rejects heat from compressed refrigerant vapour to outside air, causing it to condense to liquid. Airflow blockage or fan failure raises high-side pressure and reduces cooling.

The heat exchanger inside the cabin where liquid refrigerant boils and absorbs heat from air. It also dehumidifies, and its surface must be kept clean and drained to avoid odours and icing.

A high-side reservoir that stores liquid refrigerant and holds desiccant to remove moisture. A saturated drier restricts flow and must be replaced whenever the system is opened.

Removing air and moisture from a system with a vacuum pump to a specified deep vacuum, held to confirm no leaks. It is essential before charging and protects the compressor and expansion device.

Pressure below atmospheric, measured in microns or millibars, used to boil off moisture and prove system tightness. A vacuum that rises after isolation indicates a leak or trapped moisture.

An electronic instrument measuring deep vacuum in microns, far more precisely than manifold gauges. It confirms evacuation is complete and that the system holds vacuum.

A sight glass element that changes colour to show water content in refrigerant or oil. It warns of moisture ingress that could form acids and damage the system.

A controlled check of vent temperature, pressures and airflow against manufacturer specifications at set ambient and engine conditions. It confirms the repair restored cooling before handover.

The final stage of setting a repaired system into service, including charge verification, control calibration, function checks and recording results for the customer and workshop records.

An electromagnetic coupling that engages the compressor pulley with the drive shaft on command from the control module. It protects the belt and allows the system to cycle.

A sensor that opens or closes circuits at set refrigerant pressures to protect the compressor and fans. Three-level types signal low charge, fan control and overpressure cut-out.

A stored diagnostic trouble code set by the air conditioning or body control module when a circuit or sensor reads out of range. It guides testing with a scan tool and wiring diagram.

A pleated filter that traps dust, pollen and particles from air entering the HVAC case. A clogged filter reduces airflow, causes window misting and stresses the blower.

An electric fan that moves air through the HVAC case, often controlled by a resistor pack or PWM module. Speed faults usually trace to the resistor, module or motor brushes.

A movable flap that directs conditioned air to windscreen, face or foot outlets. Actuator or calibration faults leave air stuck at one outlet or prevent defrost selection.

A refrigerant other than the original R-134a or R-1234yf, such as R-744 carbon dioxide or blends. It requires different equipment, pressures and safety procedures and must never be mixed with the original charge.

A low-GWP hydrofluoroolefin refrigerant used in newer vehicles, classified as mildly flammable (A2L). It needs dedicated service equipment, leak detection and ignition-source precautions.

A safety classification for mildly flammable refrigerants with low burning velocity. Workshops must control ignition sources, ventilate, and use equipment rated for A2L when servicing such systems.

A device that analyses a gas sample to confirm refrigerant type and detect contamination or mixed gases. It prevents cross-contamination of recovery cylinders and service equipment.

Documentation of work performed, refrigerant type and quantity recovered or charged, leak checks and test results. It supports traceability, warranty claims and regulatory compliance.

Explaining the fault found, work done, costs and any advice on use or follow-up to the vehicle owner. Clear, jargon-free communication prevents disputes and builds trust.

Planning and overseeing technicians' work so that safety rules, equipment use and quality standards are met. It includes allocating jobs, checking competence and maintaining records.