Heat pump Icing

Heat pumps provide heating and cooling all in one system. They often offer lower-priced household climate control than other types of furnaces and air conditioners. Like any other mechanical device, however, heat pumps can malfunction. If the heat pump ices up, it may indicate a problem that could be as easy to fix as cleaning up debris around the exterior unit.

How Refrigerants Work

A heat pump can ice up because it uses a refrigerant, as a heat pump is essentially a refrigeration system. A compressor and two coils of copper tubing--one indoors and one outdoors--create a system that both cools and heats a home. In winter, the liquid refrigerant in the outdoor coils takes heat from the air and evaporates it into a gas. The refrigerant condenses into a liquid when it reaches the inside coils. That heat is then released into the house. In the summer, the refrigerant evaporates in the inside coils, taking heat from the indoors. The gas is compressed and transferred to the outdoor coils where it condenses, releasing the heat from the house into the outdoor air. Compressing the refrigerant causes it to condense at a higher temperature outside and evaporate at a lower temperature inside.

When the system is low on refrigerant, the coils cool down unevenly, which can cause icing. Part of the coil gets very cold and moisture in the air begins to condense on the coil, causing ice to form. The ice then acts as an insulator, making the problem worse. This is the most common reason a heat pump ices. It is not a problem you can fix yourself. It is illegal for a person who is not certified by the U.S. Environmental Protection Agency to handle refrigerant, which is a hydrofluorocarbon, one of the compounds responsible for global warming.

Winter Weather

It is normal for heat pumps to ice up in the winter, according to Climate Makers. The entire coil can be covered with frost. The heat pump has a defrost cycle that automatically defrosts the coils and keeps the unit working properly. A heat pump that is completely covered in ice for more than a short time, however, has a problem. The first thing to do is to clear the ice. Hannabery HVAC suggests turning the thermostat to auxiliary heat (which causes the unit to heat the house using electric coils only) or off. Pour warm or hot water over the unit to melt the snow and ice. Once the unit is ice-free, turn the thermostat back to the regular heating setting. If the heat pump ices up again, call a repair service.

Mechanical Causes

Icing could indicate a problem with the heat pump itself, according to Inspectapedia. The air flow around the cooling coil may be blocked due to debris, a dirty air filter or collapsed duct insulation. A defective or malfunctioning refrigerant metering device can block any refrigerant from moving through the system. Alternatively, dirty blower fan blades or a broken blower fan can prevent air from moving across the cooling coil. Other possible causes of icing in the summer are a broken thermostat, a defective blower belt or dirty coils.