Superheat, Subcooling & System Tuning

Two temperature measurements, taken with a clamp-on probe and the service gauges, reveal more about a refrigeration system's health than any other test: superheat and subcooling. Between them they diagnose refrigerant charge, expansion valve behaviour, and how much of the machine's heat exchangers are actually doing their job. Anyone responsible for refrigeration plant, even without touching a spanner, should understand what these numbers mean and roughly where they should sit.