Refrigeration and Air Conditioning Appliances
What this domain tests
Refrigeration and Air Conditioning Appliances covers the vapour-compression cycle, refrigerator and room-AC components, refrigerant safety, leak testing, evacuation and charging.
Core rules
- The cycle has four main changes: the compressor raises pressure and temperature; the condenser rejects heat; the expansion device drops pressure; the evaporator absorbs heat. Frost pattern, suction pressure and condenser airflow are diagnostic clues.
- Common refrigerants include R600a (flammable), R32 (A2L, mildly flammable) and R410A. Never mix refrigerants, never vent to atmosphere, and recover refrigerant with approved equipment.
- A hermetic system must be evacuated before charging; moisture and air cause acid, ice blockage and poor cooling. Charge by weight or by manufacturer's data, not by guess.
- For a split AC, check filters, indoor and outdoor coils, drain, fan motor, capacitor, service valves and indoor/outdoor communication. Electrical work requires isolation and capacitor discharge.
Worked example
A refrigerator runs continuously but the cabinet is warm. The condenser is hot and dusty, the door seal is poor, and there is no frost on the evaporator. Reasoning: first restore airflow and seal, then check for a refrigerant leak. A lack of frost plus low suction pressure suggests undercharge or a leak; a restriction often shows frost at the capillary. Repair the leak, evacuate and recharge by weight.
Traps that cost marks
Topping up refrigerant without finding the leak; charging without evacuation; using the wrong refrigerant or oil; ignoring a dirty condenser; and working on a flammable refrigerant near a spark.