Heat Pump Installation and Commissioning
Installation and commissioning questions focus on decisions made before and during startup: load calculation, line-set sizing, brazing, evacuation, electrical supply, condensate, ductwork, clearances, and documented performance checks.
Before startup
- Size from a room-by-room load calculation, not from the old unit's tonnage. Confirm the indoor coil matches the outdoor unit and the refrigerant type.
- Follow the manufacturer's line-set diameter, maximum length, and vertical separation. Insulate the suction line fully; support it and avoid oil traps.
- Purge with dry nitrogen while brazing. Use a filter drier, pressure-test with dry nitrogen, then evacuate. A standing vacuum test (isolate the pump and watch for rise) confirms no leak or moisture.
- Verify disconnect size, breaker, wire gauge, ground, and low-voltage conductor count. Trap and slope the condensate line; check secondary drain or float switch.
Commissioning
- Measure external static pressure and airflow before judging charge.
- Weigh in charge when the line set exceeds the factory charge; use the nameplate adjustment per foot of liquid line.
- Check heating and cooling operation, reversing-valve changeover, defrost initiation/termination, auxiliary heat, emergency heat, and safety lockouts.
- Record indoor/outdoor temperatures, pressures, superheat/subcooling, amp draw, and voltage.
Worked example
A unit has a 15-ft factory charge and a 50-ft line set. The additional length is 35 ft. At 0.6 oz per foot of 3/8-in. liquid line, add 21 oz. Weigh that in after evacuation, then verify subcooling; do not rely on the gauge reading alone.
Traps
Do not commission without airflow verification. Do not use the old line set's size without checking capacity and oil return. Do not skip the vacuum decay test or leave nitrogen in the system.