Heating, Ventilation, and Air Conditioning
Core concepts
Understand the refrigeration cycle: compressor, condenser, expansion device, and evaporator. Know pressure-temperature relationships, refrigerant types, and the purpose of the receiver-drier or accumulator. Be able to explain how the blend door, blower motor, and heater core deliver cabin comfort. Know safe handling of refrigerant and the requirement to recover, recycle, and recharge rather than vent.
Traps to expect
Questions often confuse high-side and low-side pressures. High-side pressure too high can indicate overcharge, a restricted condenser, or a failed condenser fan; low-side pressure too low can indicate undercharge or a restriction. Another trap is assuming a compressor is bad when the system is simply low on refrigerant and the low-pressure switch has cut it off. Also remember that moisture in the system forms acid and ice, so the drier must be replaced when the system is opened.
Worked example
A system cools poorly, low side is low, and high side is low. Rule of thumb: both sides low usually means undercharge or a restriction; both sides high usually means overcharge or poor condenser airflow. Here, check for leaks and recharge by weight.
Study strategy
Practice reading a manifold gauge set, identifying components on a diagram, and explaining refrigerant recovery procedures.