My Window Unit and Heater Froze on the Outside

Air Conditioner Systems

• Window air conditioning units operate in much the same way as any other refrigeration system. In effect, air conditioner units remove warm air from a room environment and deliver cool air in its place. Refrigerant liquids, such as Freon, have the ability to absorb heat gases into liquid form. Once absorbed, the unit cools the liquid in a cooling coil and blows air across the coil to produce cool air. Refrigerant liquids flow through a series of coils that run from an air handler device to a condenser device. The condenser transfers the heat from the refrigerant into the outside air, while the air handler delivers cool air into the room environment.

Heat Pump Systems

• It’s not uncommon for a heat pump system to provide for a home’s heating and cooling needs. The heat pump, in and of itself, can pump heat into the house or out of the house. Much like air conditioning systems, heat pumps use a condenser unit, an air handler device and a refrigerant liquid. During cold months, the condenser unit absorbs heat from the outside air and sends it to the air handler device. The air handler then directs heated air into a home’s ductwork and vents. During warm months, the air handler device delivers warm air to the condenser for release into the outside.

Evaporator and Cooling Coils

• As window unit air conditioners and heat pump heating systems work off of the same general processes, problems involving freezing on the outside often result from similar causes. Evaporator and cooling coils contain cold refrigerant materials. Depending on the time of year, areas where these coils enter the condenser unit become prime areas for condensation to form. Under normal operating conditions, air blows across these areas and prevents excess condensation from forming. In cases where not enough air moves across coil entry points, condensation buildup will eventually turn to ice and freeze over. Covering coil lines with insulation materials may help prevent freezing.

Metering Devices

• Refrigeration and heat pump heater systems rely on metering devices to deliver the needed amounts of refrigerant into the cooling and evaporator coils. For smaller appliances, such as window air conditioner units, capillary tubes regulate the amount of refrigerant that enters the coils. For larger systems, thermal expansion valves regulate refrigerant amounts based on the temperature of the refrigerant moving through the coil. When a capillary tube or a thermal expansion valve malfunctions, window units and outdoor heat pump condenser units can ice over. Replacing a faulty metering device may remedy the problem.