Which two conditions typical factors in initiation of a defrost cycle in a heat pump?

Which two conditions typical factors in initiation of a defrost cycle in a heat pump?

• A. Time and ambient
• B. Humidity and pressure
• C. Time and temperature
• D. Voltage and current

Answer: (C)

Defrost cycles are typically started based on two signals: a timer and a temperature condition. The timer provides periodic defrost events, preventing excessive frost buildup when the outdoor coil is exposed to freezing moisture. The temperature input monitors the outdoor coil temperature (often the coil or a related sensor) to detect when frost has formed enough to impair heat transfer and needs to be melted. Together, these two signals—time and temperature—drive when a defrost cycle begins. Humidity or pressure aren’t used as primary triggers, and voltage/current pertain to power, not cycle initiation.

Defrost cycles are typically started based on two signals: a timer and a temperature condition. The timer provides periodic defrost events, preventing excessive frost buildup when the outdoor coil is exposed to freezing moisture. The temperature input monitors the outdoor coil temperature (often the coil or a related sensor) to detect when frost has formed enough to impair heat transfer and needs to be melted. Together, these two signals—time and temperature—drive when a defrost cycle begins. Humidity or pressure aren’t used as primary triggers, and voltage/current pertain to power, not cycle initiation.