How Concerned Should You Be If Your Home’s Heat Pump Freezes Over?


How concerned should you be if your heat pump freezes over?  Maybe not very—at least, not just yet. If a light coating of frost appears on the heat pump’s external coils, as well as the refrigerant lines that run into the house, it probably just means the outdoor temperature’s dropped to 40 degrees or below and the amount of water vapor in the air is above 70 percent. Since the heat pump coil typically runs about 20 degrees lower than the outdoor temperature, dew forming on the cold coil and refrigerant conduit freezes into a dusty layer of frost.

HVAC systemTwo caveats are important to keep in mind when your heat pump freezes over:

  • Frost should be a temporary issue. Heat pumps incorporate defrosting technology to automatically eliminate frost on the coils. A reversing valve in the system redirects warm refrigerant flow back the outdoor coil and melts the frost. These systems may be actuated at regular intervals by a timer or controlled by a microprocessor that senses frost conditions.In any case, the appearance of frost on the heat pump shouldn’t linger for more than a couple of hours. If frost continues to accumulate beyond that time frame, a defect in the defrost cycle may have occurred.
  • Ice is another matter. A thick coating of ice on the coil differs from a layer of frost. Ice forming on a heat pump may eventually encase the entire unit and obstruct airflow through the coil. Usually, the system will either run non-stop or automatically shut down.If obvious causes such as falling sleet or freezing rain are ruled out, thick ice accumulation on a heat pump indicates potential malfunctions such as a low refrigerant charge, which is usually indicative of a leak, a defective defrost timer or sensor, or a stuck reversing valve.

For anything more than light frost accumulation that melts within a few hours, contact a qualified HVAC service provider.

If the heat pump freezes over in your Boston area home, call Rodenhiser Plumbing Heating & Air Conditioning.

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