Core: Servicing and Maintenance of Domestic Refrigeration and Air Conditioning Units
Scope
This domain covers planned preventive maintenance: cleaning, inspection, charge verification and documentation on units already in service.
Standard PM sequence
- Record before-readings: ambient, suction and liquid pressures, air-on/air-off temperatures, amp draw.
- Isolate and tag out; remove and wash filters.
- Clean the evaporator and condenser coils - apply coil cleaner, rinse at low pressure, keep electrics and insulation dry.
- Clean the blower wheel and drain pan, flush the drain line, restore the trap.
- Check electrical terminals for tightness, contactor pitting, capacitor capacitance against rating, compressor amps and insulation resistance.
- Verify charge by superheat (fixed orifice) or subcooling (TXV); record after-readings and advise the customer.
Why it matters
A fouled condenser raises discharge pressure and current while cutting capacity. A fouled evaporator drops airflow, giving low suction pressure and an iced coil. Neither is fixed by adding refrigerant.
Worked example
R-22 unit, liquid pressure 200 psig. The chart gives a 100 °F saturation temperature for that pressure; a contact thermometer reads 88 °F on the liquid line. Subcooling = 100 − 88 = 12 °F, which sits inside a typical 8–12 °F design band, so with a clean condenser and normal amps the charge is acceptable. If subcooling were 20 °F with high discharge pressure, suspect overcharge or a liquid-line restriction instead.
Traps
Topping up refrigerant to cure an iced coil caused by airflow; wetting control boards during coil cleaning; reusing a swollen or wrong-voltage capacitor; over-tightening flare joints on reassembly; leaving no written before/after record.