Installation, commissioning, servicing, troubleshooting and preventive maintenance
What this domain tests
Site preparation, pipe work, pressure testing, evacuation, charging, commissioning checks and the systematic servicing, troubleshooting and preventive-maintenance routine expected in the trade.
Core rules
- Pipe work: cut with a tube cutter, deburr, anneal before bending, keep bends reasonable, insulate the suction line and fit a liquid line filter-drier. Braze with dry nitrogen purging, otherwise copper oxide scale forms inside and later blocks the capillary or drier.
- Pressure test with dry nitrogen, commonly 1.5 times working pressure held for 24 hours with a gauge on the line; never use oxygen or refrigerant as the test gas.
- Triple evacuation with nitrogen breaks, down to 500 micron and held at least 30 minutes with the pump isolated. A rising micron gauge means moisture or a leak.
- Charge by weight on critical systems, otherwise by superheat (fixed orifice) or subcooling (TEV). R410A must be charged as liquid.
- Commissioning: voltage, current, insulation resistance, earthing, fan rotation, airflow, drain flow, thermostat and safety cut-out operation, then record the readings.
- Preventive maintenance: clean condenser and evaporator, straighten fins, tighten terminals, clean drain, inspect contactor pitting, measure insulation resistance, verify charge, oil condition, belt tension and filters.
Worked example
An R410A split unit runs at 35 °C ambient. Liquid line temperature is 41 °C and the condensing saturation temperature from the high-side gauge is 45 °C, so subcooling = 45 − 41 = 4 K. The target is 8–10 K, so the charge is low. Add liquid refrigerant in small steps, letting the system stabilise between steps, until subcooling reaches about 9 K, then recheck superheat and running current.
Traps
Oxygen pressure testing, which is an explosion risk; skipping the nitrogen purge; accepting a vacuum that holds on the manifold gauge but not on a micron gauge; overcharging to make suction look wet; topping up a leaking system without locating the leak.