Refrigeration Systems and Components
Core concepts
Know the function and typical failure modes of each component. The compressor (reciprocating, scroll, screw, centrifugal) raises pressure; capacity control may be via unloading, VFD or cylinder bypass. The condenser rejects heat - air-cooled, water-cooled or evaporative - and must be sized for the design ambient or wet-bulb. The evaporator (DX, flooded, or pumped) absorbs heat; the metering device (thermostatic expansion valve, electronic expansion valve, capillary tube, or fixed orifice) controls refrigerant flow to maintain superheat.
Accessories matter: filter-driers remove moisture and acid, liquid line sight glasses show flash gas, accumulators protect against liquid slugging, oil separators return lubricant, and receivers store liquid charge. Understand the difference between a pump-down cycle and a pump-out cycle, and the role of low- and high-pressure switches, defrost controls and crankcase heaters.
Traps in questions
- A TXV controls superheat, not evaporator pressure or room temperature directly.
- A sight glass showing bubbles does not always mean undercharge - it can indicate a restriction or flash gas from pressure drop.
- Liquid slugging damages compressors; suction accumulators and properly set superheat prevent it.
- Condenser fouling raises head pressure and reduces capacity; it does not lower suction pressure directly.
Rule of thumb
Typical TXV superheat setting is 5–8 K at the evaporator outlet. If measured superheat is far outside this band with normal pressures, suspect the valve or bulb charge first.
Worked example
A system shows high head pressure, normal suction pressure and a clear sight glass. Condenser approach (condensing temperature minus ambient) is 18 K against a design of 8 K. Diagnosis: condenser heat-rejection problem - check airflow, fan, coil fouling and refrigerant overcharge before touching the TXV.