Refrigeration and Air Conditioning Appliances
Refrigeration and Air Conditioning Appliances
Refrigeration and Air Conditioning Appliances tests the vapour-compression cycle, refrigerant handling and the servicing of refrigerators and room air conditioners.
Core rules and concepts
- Vapour-compression cycle: the compressor raises pressure and temperature; the condenser rejects heat; the expansion valve or capillary drops pressure; the evaporator absorbs heat. The refrigerant changes state, not the air.
- Refrigerants include R-134a, R-600a (isobutane, flammable) and R-32 (flammable, higher pressure). Never mix refrigerants; recover, evacuate and charge by weight.
- 1 tonne of refrigeration = 3.517 kW of cooling. COP = cooling effect ÷ compressor work input. A 1.5 TR air conditioner provides about 5.28 kW of cooling.
- Window and split air conditioners have a compressor, condenser, fan, capillary or expansion device, evaporator, filter and controls. Split units separate indoor and outdoor sections.
- Servicing: clean filters and coils, check fan motor and capacitor, leak-test, vacuum before charging, check pressures and current, and verify drainage.
Worked example
A 1.5 TR split air conditioner has a cooling capacity of 1.5 × 3.517 = 5.28 kW. If its EER is 3.2, electrical input = 5.28/3.2 = 1.65 kW, so current at 230 V is 1650/230 = 7.2 A. A clamp reading much higher suggests a failing capacitor, dirty condenser or overcharge. Reasoning: cooling capacity is not the same as electrical power; use EER to connect them.
Traps that cost marks
- Adding gas without finding the leak.
- Mixing refrigerants or charging by guesswork.
- Ignoring flammable-refrigerant warnings for R-600a and R-32.
- Cleaning a coil with the unit live.