Commissioning, Charging, and Performance Verification
Commissioning, Charging, and Performance Verification
This domain tests how to prove a heat pump is installed correctly and charged to manufacturer specifications. It covers weighing charge, superheat and subcooling methods, airflow verification, electrical measurements, and recording performance in both modes.
Core rules
- Follow the manufacturer charging chart and required conditions. Many systems are charged by subcooling in cooling and by weight or superheat in heating; some inverter systems require weigh-in only.
- Subcooling = condensing temperature minus liquid-line temperature. Convert condensing pressure with the P-T chart. Target subcooling is often 8-12 degrees F for a TXV system, but use the data plate.
- Superheat = suction-line temperature minus evaporating temperature. Fixed-orifice systems often use superheat; target varies with indoor wet bulb and outdoor dry bulb.
- Verify airflow before charging. Measure static pressure and temperature split; check blower speed and filter. Low airflow makes subcooling read high and superheat read low or erratic.
- Record line voltages, compressor amps, capacitor microfarads, pressures, temperatures, and delta T. Compare to nameplate and manufacturer data.
Worked example
A TXV system holds 250 psig condensing pressure; an R-410A P-T chart gives 118 degrees F condensing. Liquid-line temperature is 108 degrees F. Subcooling = 118 - 108 = 10 degrees F. If the chart calls for 10 degrees F and airflow is correct, charge is acceptable. If subcooling is 4 degrees F, add refrigerant slowly and recheck after stabilization.
Traps
Do not charge to a cold, sweating suction line. Do not use superheat alone on a TXV system. Do not check charge with a low indoor load or blocked coil. Do not ignore compressor amp draw and voltage unbalance.