Cooling Systems and Components
What the exam expects
Know the compressor families (reciprocating, scroll, rotary, screw, centrifugal), how each handles liquid and pressure ratios, and what failures look like. Understand metering devices: thermostatic and electronic expansion valves, fixed orifices and pistons, capillaries, and automatic expansion valves - and how each responds to load change. Know the accessories: filter driers, sight glasses, receivers, accumulators, mufflers, crankcase heaters, and head-pressure controls.
Condenser types matter: air-cooled, water-cooled, evaporative, and cooling towers, plus economizers and low-ambient strategies. For heat pumps, know the reversing valve, defrost termination, and the fact that the outdoor coil becomes the evaporator in heating mode.
Traps
- Adjusting a TXV on a system that is simply undercharged or has restricted airflow.
- "Hunting" superheat caused by an oversized valve, not by charge.
- Confusing a liquid-line restriction (high subcooling, low head) with overcharge.
- Using the wrong orifice size when converting refrigerant.
- Overlooking a dirty condenser coil as the cause of high head pressure.
Worked example
A condenser with an 8°F approach (saturated condensing temperature minus outdoor ambient) is healthy; 25°F suggests a dirty coil, bad fan, or non-condensables. On a 95°F day with 125°F saturated condensing temperature and 30°F approach, clean and verify airflow before touching charge - the subcooling reading will be meaningless.