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As cold weather sets in this winter, your home’s heat pump will be working on overdrive keeping you and your family cozy and warm. When temperatures drop, it is not uncommon for your heat pump to ice up. In fact, it is perfectly normal for the unit’s coil to become covered in white frost. During certain extreme weather conditions, it may even become coated in ice.

However, it is not normal for the entire unit to be completely encased in ice, especially for an extended period of time. If your heat pump is coated in ice, it is an indication that there is something seriously wrong. To avoid serious damage to your heating equipment, the problem should be quickly resolved.

What is a Heat Pump?

In technical terms, a heat pump is a mechanical compression cycle refrigeration system. This system can be reversed to heat or cool a specified space. In this specialized system, a compressor works to circulate a refrigerant that absorbs heat from the surrounding area. The heat is then released to another area, either heating or cooling the specified space.

What is Normal?

During the cold winter months, your heat pump will naturally ice up, periodically initiating a cycle to defrost the coils. This process ensures unit continues to run efficiently.

If the coils become frozen over and blocked with ice, proper heat transfer between the refrigerant and outside air is inhibited. With excessive ice build-up damage to the fan blades can occur. Also, heavy ice can crush the outdoor coils, leading to potential refrigerant leaks.

How the Defrost Cycle Works

The unit will automatically switch to a defrost cycle to prevent the unit from developing a dangerously thick layer of ice. In defrost mode, a reversing valve is engaged that switches the system into air conditioning mode. In air conditioning mode, the outdoor evaporator becomes the condenser and the outdoor fan shuts off. Then the high pressure refrigerant circulating through the outdoor coil gets warm, causing the ice build-up to melt. Simultaneously, back-up heat powers up, offsetting cold air blowing through the vents in your home.

Different systems have different methods for engaging in defrost mode. Some use mechanical timers that work in combination with a defrost thermostat. Other systems use solid-state control modules with temperature sensors. The most sophisticated systems a Demand Defrost system. This technology makes calculations based on the temperature outside, the refrigerant temperature in the coil, and the system run time.

What Causes a Heat Pump to Ice Up?

There are several reasons a heat pump may develop excessive ice build-up. Understanding what exactly is causing your system to freeze up is essential to getting the proper service for your system.

Refrigerant Levels

Every HVAC system needs refrigerant to operate properly. Refrigerant is what transfers heat into or out of your home, depending on whether your system is set to heat or cool the space. In summer, the heat pump moves heat outside. During cold weather, the heat pump moves the heat inside keeping your living spaces comfortably warm.

If your system lacks the proper level of refrigerant, it cannot properly transport heat. A heat pump does not use up refrigerant. Instead, it circulates continuously. If your system is running low on refrigerant, it is most likely due to a leak.

If you suspect your system is low on refrigerant, it will need to be serviced by a certified technician. He or she can check for leaks, repair any that are found, and refill your system with refrigerant.

Things You Can Fix Yourself

If your heat pump is icing up, it doesn’t necessarily mean costly repairs. Sometimes ice is caused by common problems that are easily fixed by the homeowner. These situations include:

A blocked outdoor coil. If your coils are blocked by leaves, debris, or snow drifts it could disrupt air flow and cause ice to build up on the unit. Clear all blockages to ensure proper air flow.

Leaking gutters. If your home has blocked gutters, it could cause water to drip onto your heat pump. In cold weather this could produce undue ice build up. Make sure to keep your gutters free form debris to protect your unit from dripping water.

Freezing rain. Wintry mixes, sleet, and freezing rain can cause the top of unit to freeze over. Once the top freezes, it is more likely to develop an icy coating over the rest of the heat pump. This situation may not need professional attention. However, if the ice builds up on the unit, it could damage your system. You might consider turning off the system until the ice melts.

Things That Require Professional Attention

Some causes of heat pump ice build-up require a service call. If these occur, don’t hesitate to call your local HVAC professional for help. These situations include:

  • Damaged defrost timer
  • Broken defrost thermostat or sensor
  • Bad defrost relay
  • Stuck reversing valve
  • Busted outdoor fan motor