When outdoor coils on a heat pump freeze in winter, it usually means a professional service call is in order. Minor events such as leaves obstructing airflow to the outdoor coil can cause a freeze-up, as can heavy freezing rain or sleet. However, recurrent outdoor coil icing usually points to a problem elsewhere in the system.
Technology in a heat pump dictates that an outdoor coil will naturally accumulate ice under certain circumstances. Frigid refrigerant is conveyed through coil tubes exposed to outdoor winter air. When temperatures dip and humidity rises, icing is the inevitable result. The presence of ice often does not indicate a coil malfunction, but a failure of the systems designed to keep the coils defrosted as ice accumulates. In most cases, your local HVAC contractor can diagnose the problem quickly
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Heat pumps utilize defrost technology that regularly warms the outdoor coil to keep it ice-free in sub-freezing temperatures. The defroster actuates the reversing valve, altering the flow of refrigerant so it extracts warmth from inside the home and conveys it to the outdoor coil. Simultaneously, the outdoor coil fan shuts down. This infusion of heat warms the outdoor coil and melts the ice. While defrosting is occurring, electrical resistance coils temporarily provide backup heat to maintain the flow of warm air inside the home.
Defrosting may be initiated in two ways. Older models incorporate a timer in conjunction with an external thermostat. When the temperature drops below freezing for a preset time, defrost mode is activated whether or not icing has actually occurred. New heat pumps use a solid-state controller module to sense outdoor temperature as well as the refrigerant temperature and calculate the exact time to start defrosting and how long it should continue.
Possible malfunctions in the heat pump defrosting circuit may include:
- Defective controller or timer
- Defective thermostat
- Defective defroster relay
- Stuck reversing valve solenoid
- Insufficient refrigerant charge
- Refrigerant obstruction or restriction
Since 1952, Hansberger Refrigeration and Electric Co. has kept Yuma area homeowners comfortable in all seasons. If coils on a heat pump freeze this winter, contact us for fast professional service.
Our goal is to help educate our customers in Yuma, Arizona about energy and home comfort issues (specific to HVAC systems). For more information about frozen heat pumps and other HVAC topics, download our free Home Comfort Resource guide.
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