HVAC Procedure and Performance Guide

Adjust defrost cycle on heat pump

Training for this procedure can be found in these courses:

                         131 – Oil Heat l  and  161 – Boilers l


Defrost cycle must be adjusted according to manufacturer’s specifications.  Defrost cycle must prevent icing of heat-pump outdoor coil during cold weather and must operate only when needed.  Applicable safety procedures must be followed.


  1. Review manufacturer’s specifications.
  2. Determine type of defrost initiation system (time, temperature, air-flow, or combination) and termination system (time, temperature, or combination).
  3. Collect tools, equipment and materials.
  4. Put on safety and protective equipment and apparel.
  5. Remove access cover(s).
  6. Determine if all timers are synchronized and if time cycles are correct; adjust to manufacturer’s specifications.
  7. Measure coil temperatures and/or air-flow and adjust initiation temperature control and/or air-flow switch to manufacturer’s specifications.
  8. Measure coil temperatures and adjust termination temperature control to manufacturer’s specifications.  (Note:  If components (timers, switches and thermostats) are not adjustable and defrost cycle is not correct, replace defective components in lieu of making adjustments noted in Steps 6, 7 and 8).
  9. Replace access cover(s).
  10. Leave equipment in required operating status.
  11. Remove safety and protective equipment and apparel.
  12. Gather tools, equipment and leftover materials, and leave work site clean.