Pick a symptom. Work through it like a tech would.
Symptom-first fault finding. Choose what the system is doing, then work through possible causes, what to check, what the readings should tell you, and your next step.
Low Suction Pressure
Suction pressure is below normal for the refrigerant and box temperature.
Work throughElectrical Fault
System has an electrical or control fault — won't run or runs intermittently.
Work throughNot Cooling
The system runs but the space isn't pulling down to setpoint — or not cooling at all.
Work throughEvaporator Icing
Ice building on the evaporator coil.
Work throughCompressor Won't Start
Compressor doesn't attempt to start, or hums and cuts out.
Work throughShort Cycling
Compressor starts and stops too frequently.
Work throughLow / Zero Superheat
Superheat is too low or zero — liquid reaching the compressor (floodback risk).
Work throughExcessive Subcooling
Subcooling is higher than normal — too much liquid stacked in the condenser.
Work throughPoor Capacity
System runs but can't keep up with the load — capacity is down.
Work throughHigh Head Pressure
Discharge pressure is above normal for the refrigerant and ambient.
Work throughExcessive Superheat
Superheat is higher than it should be — the evaporator is starved.
Work throughHigh Box Temperature
Box is warmer than setpoint and won't pull down.
Work throughUnusual Compressor Noise
Compressor is making knocking, rattling, or humming noises.
Work throughLow Subcooling
Subcooling is low — little liquid reserve at the metering device.
Work throughCompressor Trips
Compressor starts but trips on overload or a safety control.
Work throughPoor Condenser Performance
Condenser isn't rejecting heat properly — head pressure creeps up.
Work throughPoor Evaporator Performance
Evaporator isn't absorbing heat — box won't pull down.
Work through