If your heat pump freezes over, it’s telling you something important. While light frosting may come and go on an outdoor coil in winter, thick ice formation on an indoor or outdoor heat pump coil is never normal in any season. Usually, it’s a symptom of imbalance somewhere in the system. Heat pump energy efficiency and performance are severely diminished by coil icing. In extreme cases, the unit may shut down entirely. Here are typical reasons a heat pump freezes over, and what you can do about it.

Insufficient Airflow

The temperature of a heat pump indoor coil in cooling mode normally remains above 40 degrees Fahrenheit. If system airflow drops below specifications, however, heat transfer declines and coil refrigerant temperature plunges. Condensation on the coil freezes, initiating the cycle of ice accumulation. Common reasons for low airflow include:

  • Dirty air filter. A clogged filter reduces air volume through the coil, potentially causing icing. Changing the air filter is a simple DIY task—a qualified HVAC service tech can show you how if you don’t know—and should ideally be performed monthly.
  • Closed or obstructed vents. Balanced system airflow depends on open supply and return vents in individual rooms. If one or more vents are manually shut or blocked by furniture, drapes or other obstructions, airflow through the coil may be insufficient to prevent icing. Keep all vents clear and don’t close vents in unoccupied rooms.

Low Refrigerant

Proper refrigerant charge is a critical balance. As refrigerant pressure declines below specifications, refrigerant temperature drops, too. Coil icing soon follows. Low refrigerant charge is usually caused by leakage. A qualified HVAC service technician has the equipment and expertise to pinpoint and repair refrigerant leaks, then restore the refrigerant charge to manufacturer’s specifications.

Defective Defroster

If light winter frosting on an outdoor coil accumulates into a layer of thick ice, the heat pump’s automatic defroster may have failed. Professional troubleshooting is required to isolate the problem, replace defective components and verify proper repair.

For qualified service if your heat pump freezes over, in the greater Cincinnati area, contact Apollo Home Heating, Cooling and Plumbing.

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