Maintenance, Servicing and Troubleshooting
Planned maintenance
A schedule earns marks: clean or replace filters monthly on dusty sites, clean coils, flush the condensate drain, check fan blades and bearings, tighten terminals, inspect contactor contacts for pitting, test capacitors, measure compressor current against nameplate RLA, verify charge by superheat or subcooling, and log everything. Maintenance prevents the failures that troubleshooting questions describe.
Systematic fault finding
Work from symptom to system, not from guess to gas cylinder.
- No cooling with compressor running: dirty filter or coil, low charge, restriction, thermostat setting.
- Compressor hums and trips: capacitor, start relay, seized compressor, low voltage, winding fault.
- High head pressure: dirty condenser, condenser fan fault, overcharge, non-condensables, air recirculation.
- Low suction pressure: undercharge, restriction, iced evaporator, low airflow.
- Ice at the capillary inlet: moisture or restriction.
Worked example
A window unit cools poorly. Discharge pressure is high, subcooling is high at 14 K, condenser air temperature rise is high, and the coil is uniformly hot. High subcooling plus high head points to overcharge or non-condensables; the uniformly hot coil supports overcharge. Recover, weigh in the nameplate charge, and re-check. Do not simply bleed gas.
Traps
Adding refrigerant to cure a dirty condenser; diagnosing from gauges alone without temperatures; and leaving a system open to atmosphere while you fetch a part.