____________ temperature determines the defrost termination on a heat pump using time initiated temperature.

____________ temperature determines the defrost termination on a heat pump using time initiated temperature.

• A. Supply air temperature
• B. Ambient temperature
• C. Indoor temperature
• D. Outdoor temperature

Answer: (B)

In a time-initiated, temperature-terminated defrost control, the system starts defrost after a set time, but stops defrost when outdoor ambient temperature reaches a defined setpoint. This uses the outdoor air as the signal that conditions are now favorable enough for ice to melt and for normal heating to resume, so you don’t waste time defrosting longer than needed. Indoor temperature or supply-air temperature don’t reflect the conditions on the outdoor coil, so they aren’t used to end defrost. The ambient outdoor temperature is the key indicator used to terminate the cycle.

In a time-initiated, temperature-terminated defrost control, the system starts defrost after a set time, but stops defrost when outdoor ambient temperature reaches a defined setpoint. This uses the outdoor air as the signal that conditions are now favorable enough for ice to melt and for normal heating to resume, so you don’t waste time defrosting longer than needed. Indoor temperature or supply-air temperature don’t reflect the conditions on the outdoor coil, so they aren’t used to end defrost. The ambient outdoor temperature is the key indicator used to terminate the cycle.