St.Augustine

St.Augustine
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Wednesday, January 22, 2014

HEAT PUMP DEFROST CYCLE/MODE



When the weather is colder, we get a lot of call from our customers stating that they saw smoke coming out of their outside heat pump condensing unit and there is ice on the unit. My first question to them usually is, "Is it ICE, or is it FROST?" Then they usually respond that it is frost. So I explain to them that the heat pump is in the defrost cycle/mode and it was steam, not smoke, that they saw and NOT to turn the system off because this is a normal function of the heat pump system.

When a homeowner sees a puff of steam coming out of their heat pump condensing unit, and it is a cold day, the heat pump is probably in the "defrost cycle/mode". The defrost cycle/mode is a normal function of a heat pump system in colder weather. Icing/frosting on a heat pump condenser is normal in cooler weather. The outdoor unit, which is normally an air conditioner, reverses the process and becomes a heater. In the heating mode, the outdoor coil becomes cooler than the outdoor air in order to absorb heat from the outdoor air and pump it indoors. The heat pump has a defrost cycle/mode that will reverse the heat pump back to the air conditioning mode when it detects ice/frost on the outdoor coil. In the cooling mode, the outdoor coil is hot from the heat absorbed from the indoor air. The hot outdoor coil melts the ice and then the defrost control returns the heat pump to the heating mode. During the defrost cycle/mode, the indoor coil is cold, so the auxiliary heat is used to temper the cooler air.

If you see ice (about a 1/4" thick), turn your thermostat to the auxilary/emergency heat mode and call your service provider.

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about Indoor Air Quality and other HVAC topics, click here to visit our website.

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