Vehicle Air-Conditioning and Climate Control
What this domain tests
This domain covers refrigeration principles, refrigerant handling, leak diagnosis, compressor and air-distribution faults, and climate control electronics. The exam expects safe recovery and a pressure-based diagnosis, not guesswork.
Core rules
- R134a and R1234yf are different refrigerants and must not be mixed; use dedicated recovery equipment and identify the system before connecting.
- Recover refrigerant, never vent it. Evacuate the system, usually for at least 30 minutes, and check that it holds vacuum before charging by weight.
- Use the specified PAG oil; add oil only in the amount removed or specified for the replaced component.
- Typical diagnosis: low side low and high side low suggests undercharge or a leak; low side low and high side high suggests a restriction; both high suggests overcharge or poor condenser airflow; low side high and high side low suggests a weak compressor.
- Check cabin filter, blower, blend door and condenser fins before condemning the refrigeration circuit.
- Wear eye and hand protection; liquid refrigerant causes frostbite.
Worked example
An air-conditioning system blows warm. The compressor clutch cycles quickly. Gauges show low side 20 psi and high side 110 psi at 30 °C ambient. The reasoning is a low charge: both sides are low and the clutch is cycling on the low-pressure switch. The correct sequence is to recover the remaining refrigerant, leak-test with nitrogen or dye, repair the leak, replace the receiver-drier if the system was open, evacuate, hold vacuum, then charge by weight. Adding gas without finding the leak is a temporary fix and may overcharge the system later.
Traps
Venting refrigerant is an environmental offence. Overcharging raises both pressures and reduces cooling. Mixing refrigerants contaminates the recovery cylinder. Do not add oil blindly; too much oil reduces heat transfer. Do not ignore a blocked cabin filter or a stuck blend door.