Installation, Piping, and Airflow
Installation, Piping, and Airflow
This domain tests correct installation of air-source heat pumps: location and clearances, line sizing, brazing, evacuation, condensate removal, electrical supply, and airflow. The exam expects you to know why each step matters, not just the step.
Core rules
- The outdoor unit needs manufacturer clearance and free air movement; avoid recirculation and snow accumulation. The indoor unit needs service access and primary and secondary drains, with a trap on draw-through coils.
- Suction and liquid line sizes follow manufacturer tables and equivalent length. Long runs or vertical lifts may require oil traps or larger lines; never reduce line size to save copper.
- Brazing requires flowing nitrogen to prevent internal oxidation. Use a filter drier, pressure test with dry nitrogen, and evacuate to 500 microns or below; isolate the vacuum and confirm it holds.
- Airflow is typically 350-450 CFM per ton in cooling; heating airflow may differ. High static pressure reduces capacity and can freeze coils; low airflow causes high superheat and compressor overheating.
- Electrical supply must match nameplate voltage, phase, and minimum circuit ampacity; use a properly sized disconnect and breaker.
Worked example
A 3-ton system needs about 1,200 CFM at 400 CFM/ton. A flow hood reads 900 CFM. The temperature split is high and the indoor coil is frosting. The correction is airflow, not charge: check the filter, blower speed, duct restrictions, and coil. Adding refrigerant would worsen flooding and compressor loading.
Traps
Do not skip nitrogen purge; black copper oxide contaminates the system. Do not charge by pressures before verifying airflow. Do not trap a draw-through coil incorrectly or omit the secondary drain. Do not size lines by sight.