Refrigeration Cycle & Equipment
25% of this examThe vapor-compression cycle and the equipment that runs it: the four components in order, what superheat and subcooling mean, how to charge a system, and how a heat pump reverses. These are concept questions — Refrigeration & Air Conditioning Technology confirms answers, but the cycle has to live in your head.
Core concepts
Four components, one loop
Compressor (low-pressure vapor in, high-pressure vapor out) → condenser (rejects heat, vapor condenses to high-pressure liquid) → metering device (drops pressure, liquid flashes to low-pressure liquid/vapor mix) → evaporator (absorbs heat, refrigerant boils to vapor). Heat is absorbed indoors at the evaporator and rejected outdoors at the condenser.
Superheat at the evaporator, subcooling at the condenser
Superheat is how far the vapor at the evaporator outlet is above its boiling (saturation) temperature; subcooling is how far the liquid at the condenser outlet is below its condensing temperature. Each is measured at its own coil's outlet — mixing them up is the standard distractor.
The metering device decides the charging method
A TXV modulates flow to hold evaporator superheat roughly constant as load changes — so superheat can't tell you about charge. Charge TXV systems by subcooling against the manufacturer's target; charge fixed-orifice (piston/cap-tube) systems by total superheat against a charging chart.
Heat pumps add one valve
The reversing valve redirects compressor discharge gas so the indoor coil becomes the condenser in heating mode and the outdoor coil the evaporator. The same valve flips the system back to cooling briefly during defrost to melt frost off the outdoor coil.
Key facts to know cold
Where it lives in your books
The real exam is open book. Knowing which book — and which tab — answers this domain is worth as much as memorizing it.
Lookup strategy
- · Sketch the four-component loop with pressures and states before the exam starts — most refrigeration questions are answered straight off that sketch.
- · Charging-method questions hinge on one word in the stem: spot 'TXV' or 'fixed orifice' first, then pick subcooling or superheat accordingly.
Reading isn't learning — retrieval is.
65 questions in this domain, each with an explanation and source.