A Heat Pump is an air conditioner that is essentially running in reverse. In an air conditioner, there are two 'coils' that the refrigerant are circulated through. One is the condensor, (hot), the other is the evaporator, (cold). When running in air conditioning, the indoor coil is cold and we recirculate our indoor air across this coil to absorb the heat, then take it outside to the condensor coil, where we blow outdoor air across it to remove the heat.
Its a matter of heat transfer. We create an area with an 'extreme lack of heat', and absorb the heat from the air around it to transfer it someplace else.
When a Heat Pump is in heat. The indoor coil is the condensor coil, (hot), and the evaporator coil is outside. The hope is, that we can absorb heat from the outdoor air and bring it inside. The problem is, the coil will be so cold that it will frost up and if unchecked, will ice up. This keeps the unit from absorbing any heat and all you'll get is cold air in the house when running in heat.
They have a defrost system built into them that is supposed to detect when the outdoor coil is 28 deg F. Since freezing is 32, if we're at 28, we're freezing for sure. There is a sensor that is supposed to detect this. The defrost system will check the sensor every so often, (30, 60 or 90 mins depending where the jumpers are set on the board). When the board see's the sensor is 28, the unit reverses into air conditioning, thereby warming the outdoor coil and melting the frost/ice away.
WHEN THE UNIT DOES THIS, IT WILL BE IN AIR CONDITIONING AND YOU WILL, MORE THAN LIKELY GET COLD AIR INSIDE THE HOUSE AND QUITE POSSIBLY SEE STEAM COMING FROM THE OUTDOOR UNIT. DO NOT BE ALARMED! DO NOT TURN THE UNIT OFF! ALLOW IT TO RUN AND DE-ICE ITSELF PROPERLY. TURNING THE UNIT OFF WILL CONFUSE IT AND IT WILL BE LONGER BEFORE IT WILL HEAT PROPERLY!
The defrost cycle shouldn't take more than about 15 - 20 mins max. If it does take longer than this, there is more than likely a problem and you'll need someone out.
Heat pumps were not designed for a really cold climate. In cold country they will have an outdoor thermostat and it controls a set of electric heat strips. When it gets below where ever they have the t-stat set, (40 - 45deg), the heat strips would come on and assist the heat pump. Heat Pumps in the valley are typically not equipped with this option so during the rare occurances that really cold weather sets in, the heat pumps will struggle.
Unless you're prepared to spend from $300 to $800 to add electric strips and a new circuit from the electric panel, don't sweat it. Set the thermostat on a reasonable setting, (68 or below), and let it do its thing while it's really cold.
If you have other questions you can email me or call the office.
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