What a Heat Pump’s Defrost Cycle Does

In the winter, and on an especially cold winter day or night, your home’s heat pump may – and it should – go into a defrost cycle. This is good. It’s what should happen. By defrosting itself, the heat pump and the whole HVAC system will work more effectively in the cold.
There can be confusion about what the defrost cycle is. If you don’t know what’s going on, you might be thinking your heat system is broken or failing. If your machine is defrosting correctly, you have nothing to worry about. Still, this could lead you to have a concern. Here are a few things to know. You can also call an expert professional to check and inspect your HVAC system first hand.

What’s a Defrost Cycle on My Heat Pump?

When it’s on, a heat pump draws heat from the outdoor air and draws it inside to heat it. The exterior air is cooler and typically wetter, so the exterior coil functions as an evaporator. Under cold temperature and certain humidity conditions, the moisture in the air freezes on the system’s heat exchanger as the fan blows the air throughout it. This process can form frost on the outdoor coil. This layer of frost will inevitably make the heat pump run harder, and this is inefficient, so the frost needs to be removed. The defrost cycle automatically comes on and the system should remove the frost.

Exactly How Does the Defrost Cycle Defrost?

When a heat pump goes into its defrost cycle, it is running in reverse. A defrost setting tells the reversing valve to send heated refrigerant outdoors to thaw the outside coil. When the heat pump switches over, the exterior fan is turned off and the temperature of the coil increases. The time it takes to thaw the exterior coil will certainly vary, yet hea

t pumps will typically stay in the defrost cycle until the coil reaches about 58 degrees. When the system is without frost, the internal heating unit will stop, the valve will reverse and the unit will return to the usual home heating setting.

How Do I Know the Defrost Cycle is On?

If you’re inside the house, you’ll know something’s changed if the heating system isn’t heating inside and the fan is off. This will seem strange because, well, this is happening while it’s very cold outside – by design, don’t panic. With most systems, there is a light or some other symbol. If you’re outdoors near the heat pump, you can tell the outdoor fan has stopped and the compressor is running.

How Often Should the Defrost Cycle Happen?

There are a variety of aspects that influence when a heat pump switches over to the defrost cycle. The primary ones are the temperature and weather outside, the amount of heat the system is supplying inside and the overall condition of the heating system. Usually, heat pumps will defrost routinely when you have frost conditions. However, the frequency of defrosts should be no more than about every 35 minutes. The length of time the heat pump will take to  thaw can vary, too, yet ordinarily, it shouldn’t needs to take longer than 10 minutes in a cycle. The defrost cycle is meant to be enough time to thaw frost or ice, however short enough to not use too much energy or keep your home without heat coming in.

Indicators of Heat Pump Issues

If your home heat pump is defrosting too often or not keeping your house warm because it’s kicking into defrost, you may have more concerns with the pump or HVAC system.

If this has actually been happening throughout the whole life of the system, it could be an error in the installation or by the operator. In this case, start by checking the owner’s manual.

Once you’ve gone over these potential fixes, and it’s not anything you can change, it’s probably time to call the service provider or a expert technician. It could be the unit and system are wrong for the home, home size or set-up. It could be some other installation or set-up error that’s been there the whole time. A professional can assist you with right operation, sizing and any other technical issues.

If this issue is new, it may be from faulty or worn equipment, or more maintenance is required. Try some simple at-home maintenance yourself first. Change your air filters. Clean the outside parts of the system as best as possible. Make sure your heat exchanger is clear. If you’ve gone through these suggestions and are still having trouble, it’s time to contact the pros.
If you are experiencing problems with your heat pump, or any other part of your heating and cooling system, the last thing you want is to be dealing with it during winter cold.

At South End Heating and Air we specialize in HVAC and furnace repair, call us for a free consult. We’ll evaluate your system and help make recommendations for optimum value. After all, we want to keep you cool all summer long and warm in the winter. Just schedule a visit with one of our technicians to talk about how we can help with your heating needs. Would you like to learn more options our techs can help you with? Give us a call 704-684-5339.