Understanding a Heat Pump

Like an air conditioner, it can lower indoor temperatures by removing heat from the air and expelling it outside; it is also capable of extracting heat from outside air and pumping it indoors.

To do its job, a heat pump – like all refrigeration devices – takes advantage of liquid’s tendency to absorb heat as it expands and turns into a gas, giving off heat as it’s compressed into a liquid.

A split system heat pump uses two units, one outdoors and one indoors. In the outdoor unit, a fan moves air through a coil that absorbs heat. A compressor then super heats the vapor and sends it through refrigerant lines to a second coil in the furnace. There a blower pushes return air through the coil, warming the air and forcing it onto the ducts. Meanwhile refrigerant travels back to the outdoor unit to begin another full cycle through the pump.

An automatic reversing valve reverses these flows. It has to be automatic because when outside air temperatures approach the freezing mark, heat pumps tend to freeze up. When this happens, a sensor activates the reversing valve and the unit defrosts itself.

In some heat pumps, the compressor, fan, coils, reversing valve, and the blower are enclosed in a single outdoor cabinet. Only the system’s main supply and return ducts penetrate exterior walls; there is no separate furnace.

Heat Pump Problems

If the pump does not run, it could mean no power to the unit or the thermostat is not calling for heat. Check the thermostat setting, the electrical disconnect switch, and the fuses or breakers in the circuit panel. Most pumps have a reset switch in the outdoor cabinet.

If the pump has only short cycles, could mean an obstruction blocking the outdoor coil; malfunctioning blower unit; or clogged filter. Clear the outdoor coil and check the filter and blower unit.

If the pump has long or frequent defrost cycles, could mean a blocked outdoor coil causing the defrost cycle to last long than 15 minutes or to occur more than twice in an hour. Check the outdoor coils and check for accumulating leaves and trash around the unit.

If the pump has uneven heating, could mean that the heat pump is delivering a cooler flow of air than you may be used to. Also, indoor temperatures normally will drop 2 to 3 degrees when the outside temperature reaches the system’s balance point differential. This is the point at which thhoe backup heating kicks in. You need to minimize the airflow discomfort by carefully balancing the duct system. To offset the balance point differential, you may have to raise the thermostat setting in colder weather.