HVACR Core Knowledge and Skills
Domain focus
This domain tests the hands-on fundamentals a Master HP candidate uses on every heat pump: refrigerant cycle, pressure-temperature relationships, brazing and evacuation, charging, and component identification. Expect questions that combine a specification with a field measurement rather than isolated definitions.
Core rules
- Use the correct PT chart for the refrigerant; R-410A and R-32 run much higher pressures than R-22 for the same saturation temperature.
- Superheat is suction line temperature minus evaporating saturation temperature; subcooling is condensing saturation temperature minus liquid line temperature.
- Evacuate with a micron gauge at the system, isolated from the pump, and hold below 500 microns; nitrogen purge while brazing.
- Charge by weight when possible; otherwise use manufacturer subcooling or superheat targets, not rule-of-thumb pressures.
Worked example
An R-410A heat pump has 118 psig suction pressure and 52°F suction line temperature. From a PT chart, 118 psig saturation is about 40°F. Superheat = 52 - 40 = 12°F. If the manufacturer's target at these conditions is 8-12°F, the charge/expansion device is acceptable but at the upper edge; verify airflow and indoor wet-bulb before adjusting.
Traps
Using R-22 pressures on R-410A, measuring superheat at the compressor service port without accounting for line gain, trusting a manifold gauge for evacuation, and failing to flow nitrogen during brazing.