Maintenance, Troubleshooting, and Repair
Maintenance, Troubleshooting and Repair is the largest practical domain. It examines planned maintenance routines and a disciplined diagnostic process, plus the reasoning that separates a restriction from an undercharge, or a failed compressor from a failed capacitor.
Planned maintenance
Inspect and clean coils, check fan blades and bearings, belts and alignment, contactor pitting, capacitor microfarads, charge by superheat and subcooling, oil level and colour, acid and moisture indicators, relief valves, controls, insulation condition, drain pans and traps. Log readings every visit so trends appear before failures do.
The diagnostic sequence
Confirm the complaint, gather data, compare against design and nameplate, form one hypothesis, test it, repair, then verify by re-measuring. Changing parts without a reading is guesswork.
Reading the numbers
- High superheat, low suction pressure, low subcooling: undercharge or restriction. A temperature drop across the liquid-line filter drier above 1–2 K points to a restriction; no drop points to undercharge.
- Low superheat with a flooded suction and frost: overcharge, oversized valve, or low load.
- High discharge pressure with high subcooling and a condenser split above design: dirty coil, failed fan, non-condensables, or air recirculation.
- Compressor hot and tripping: check capacitor, start relay, winding resistance and insulation to ground.
Worked example
A walk-in cooler runs continuously with low suction pressure, 25 K superheat and 2 K subcooling. The liquid line is warm at the condenser outlet and noticeably cooler after the filter drier. Diagnosis: restricted drier, not low charge. Confirm with a pressure drop across the drier, then recover, replace the drier, evacuate and weigh in the nameplate charge.
Traps
- Adding refrigerant to a system with a restriction.
- Judging winding insulation with a common ohmmeter instead of a megohmmeter.
- Ignoring a compressor that runs quietly with correct winding readings - check the run capacitor.
- Restarting a compressor that tripped without finding why the overload opened.