Final answer:
During the defrost cycle of an air-to-air heat pump, the refrigerant flow reverses to defrost the outdoor coils, the outdoor fan turns off to assist the process, and supplemental electric heaters may be activated to maintain indoor comfort levels.
Step-by-step explanation:
The question concerns the defrost cycle of an air-to-air heat pump, which is an important part of its operation in cold climates. During the defrost cycle, three main things occur:
- The unit temporarily reverses the flow of refrigerant to send warm refrigerant through the outdoor coils. This process melts any frost or ice that has built up on the outside unit.
- The outdoor fan is typically turned off to increase the efficiency of the defrosting process, as it allows for higher temperatures at the outdoor coil.
- Supplementary electric heaters may be activated inside to offset the temporary loss of heating performance. This helps maintain the desired indoor temperature while the system is defrosting.
These actions are necessary to maintain efficiency and performance of the heat pump during cold months when ice can build up on the outdoor component of the unit. Defrost cycles are an example of the heat pump operating in a mode similar to that of an air conditioner, by reversing the flow of refrigerant.