Commercial Refrigeration: Low and Medium Temperature Systems
Low and medium temperature systems
Commercial refrigeration runs continuously at low or medium temperature, so controls and accessories differ from comfort cooling. Know the components: condensing unit, receiver, liquid line with filter-drier and sight glass, TEV, evaporator (unit cooler), suction line with accumulator or heat exchanger, and head-pressure controls for low ambient (fan cycling, fan speed, or flooded condenser holding minimum receiver pressure).
Know the pressure regulators: the EPR (evaporator pressure regulator) holds a minimum evaporator pressure so product does not freeze; the CPR holds suction pressure to protect the compressor; the OPR holds receiver pressure. Know defrost types (off-cycle, electric, hot gas, air), defrost termination and fan-delay controls, and the temperature difference (TD) between box air and evaporator, commonly about 10°F for medium temperature and 10-15°F for low temperature.
Traps: charging to a clear sight glass alone, adjusting an EPR without knowing the box design, calling ice on a coil low charge when it is really a defrost failure, and forgetting that a low-temperature compressor needs a crankcase heater and pump-down control.
Worked example: a cooler holding 35°F with a designed 10°F TD needs an evaporator at 25°F. Set the EPR or check the TEV so suction saturation temperature is about 25°F, then verify 4-8°F superheat at the evaporator outlet.