When a typical heat pump is operating in defrost mode, what usually happens indoors?

When a typical heat pump is operating in defrost mode, what usually happens indoors?

• A. An electric heater cycles on to temper the cold air
• B. Blower shuts off
• C. Compressor stops
• D. Indoor thermostat demand is ignored

Answer: (A)

During defrost, the outdoor coil is heated to melt frost, which means the heat pump isn’t delivering heat to the indoors in the normal way for a brief period. To keep the indoor space comfortable while this happens, many systems switch on the indoor electric resistance heater for short bursts. That supplemental heat helps offset any temporary drop in room temperature and the cooler air that can come from the indoor side during defrost. The result is a brief, tempered boost of heat inside even though the outdoor coil is being defrosted. The other options don’t fit because the compressor keeps cycling to drive the refrigerant during defrost, the blower isn’t routinely shut off just for defrost, and the thermostat demand isn’t ignored—the system simply adds electric heat to maintain comfort.

During defrost, the outdoor coil is heated to melt frost, which means the heat pump isn’t delivering heat to the indoors in the normal way for a brief period. To keep the indoor space comfortable while this happens, many systems switch on the indoor electric resistance heater for short bursts. That supplemental heat helps offset any temporary drop in room temperature and the cooler air that can come from the indoor side during defrost. The result is a brief, tempered boost of heat inside even though the outdoor coil is being defrosted. The other options don’t fit because the compressor keeps cycling to drive the refrigerant during defrost, the blower isn’t routinely shut off just for defrost, and the thermostat demand isn’t ignored—the system simply adds electric heat to maintain comfort.