Lennox Heat Pump Defrost Control Board

[Derrick Drescher]

Itis essential to understand that, for both heating and cooling, heat pumps transfer heat from one area to another. It draws heat energy from the outside air throughout colder months and moves it inside to heat your home. And to cool you off in the summer, the heat pump takes heat energy from inside your home and releases it outside.

Like auxiliary heat, emergency heat is a setting that activates the electric resistance heating strips to warm your home. However, while the auxiliary heat automatically aids the heat pump system in reaching the set temperature, the homeowner's emergency heat is turned on manually to be your primary heat source when your heat pump system malfunctions. As a result, the emergency heat mode is a significantly less efficient way of heating your home, so it should only be used when absolutely necessary.

You should turn the Emergency Heat mode on when your thermostat does not reach its desired temperature for a substantial amount of time. In this event. it is likely that your heat pump system has malfunctioned. If the heat pump system is unable to warm your home and the auxiliary heat will not satisfy the thermostat, then it is time to utilize the emergency heat mode. As soon as you turn on the emergency heat, call an HVAC professional for a heat pump repair. Otherwise, the emergency heat will run up your utility bill fast!

Homeowners should expect auxiliary heat to turn on during colder temperatures, especially under 40 degrees. Your heat pump is an amazing appliance that can efficiently extract warmth from the outdoor air and transform it into cozy comfort inside your home. However, at temperatures at or below 40 degrees, heat pumps lose quite a bit of efficiency, which can cause problems for maintaining optimal indoor conditions. This is because the heat pump cannot withdraw enough heat from the outside air fast enough to warm your home.

The auxiliary heat assists the heat pump in achieving the thermostat's set temperature. Once the set temperature is met, the heat pump and the auxiliary heat both shut off. If your Auxiliary heat is running for an extended time, you should call for a heating repair.

Homeowners should anticipate the auxiliary heat coming on when they raise the thermostat's set temperature by three degrees or more. Your heating system needs to operate with auxiliary heat to keep up with the household's new needs.

It is normal for your heat pump to accumulate some ice during colder months. However, too much ice greatly inhibits its heating and cooling capability. Therefore, your heat pump is equipped with a defrost control board that monitors defrost cycles and ice formation on the outdoor condensing unit. If the defrost control board senses the heat pump condensing unit has been too cold for too long, it signals the reversing valve to send hot refrigerant outdoors to thaw the outdoor coil. When defrost mode is activated, your heating system relies on the backup heat (aux heat) to keep your home warm. Therefore, if the heat pump is in defrost mode, you will also need to make good use of your auxiliary heat.

The auxiliary heat should only run for as long as it usually takes for your home to meet the temperature set on the thermostat. If the auxiliary heat runs either every time you turn your system on, an unusual amount of time (such as longer than 30 minutes or all day), or does not turn off, you should have your system evaluated by an HVAC pro. The auxiliary heat is an aid to your house's heat pump system, so while it is customary for it to turn on during cold weather, the homeowner should take note if it is operating for a prolonged period.

If your auxiliary heat operates for an unusually long time, you have a problem with your heat pump. It has turned on because your thermostat is struggling to reach and maintain its set indoor temperature. So, when auxiliary heat stays on, you can be certain the heat pump is malfunctioning. Read on to understand the most common reasons your auxiliary heat won't turn off.

The fan motor circulates air across the the outdoor condenser coil. Without critical airflow from the condenser fan, the heat pump will have difficulty absorbing enough heat (or releasing heat in the summer) to meet the thermostat's demands. Whether your fan motor is broken, dirty, or covered in ice, your heat pump will struggle to provide heating if proper airflow is prevented or inhibited. Therefore, if you have a faulty condenser fan motor, your auxiliary heat will be working hard this winter to keep you warm.

Refrigerant is a substance that changes states from gas to liquid. The ability to alternate between gas and liquid makes it possible to transfer heat between the outdoor coil in the condensing unit and the indoor coil in the air handler. Low refrigerant is due to a leak and means low heat absorption, causing many problems down the line, such as insufficient heating or cooling. If your heat pump system is leaking refrigerant, you are sure to face problems. As a result, your heat pump will struggle to absorb heat, thus relying on auxiliary heat.

If your heat pump is over 10 years old, it most likely uses Freon R-22. Freon-22 is a type of refrigerant has been phased out due to EPA guidelines. Check out our blog about the R-22 Freon ban to learn how it may affect you.

The compressor is part of the outdoor condensing unit. The compressor, which is powered by electricity, turns the refrigerant from a gas to a high-pressure liquid and pushes it through the outdoor condenser into the indoor air handler. If your AC compressor won't turn on, the heat pump system's ability to transfer heat will cease. Therefore the auxiliary heat will continue to run with no support from the heat pump system.

Your heating system depends on the backup heat (aux heat) during defrost mode to keep your home warm. So, if the defrost control board malfunctions, the aux heat will run extensively. Furthermore, if the defrost control board fails to defrost the accumulation of ice on your condenser, critical heat transfer will get restricted. As a result, your heat pump system will be unable to meet the thermostat's demands, resulting in the Auxiliary heat kicking in.

Every heat pump system has a reversing valve. The purpose of the reversing valve is to change the direction of the refrigerant. This is what makes the heat pump functional for both heating and cooling. However, if the reversing valve is faulty, your heat pump system may operate in cooling mode when the thermostat calls for heat. When this happens, the heat pump system pushes out cold air from your vents, while the auxiliary heat keeps trying to raise the indoor temperature. As a result, the heating and cooling functions of your heat pump are competing against each other, which will make your utility bills skyrocket!

It is nearly impossible to fully prevent the auxiliary heat from coming on when you are located in the North East United States. The heat pump system is very efficient, especially when the temperatures are above 40 degrees. However, when the temperature dips below 40 degrees, your heat pump may struggle to withdraw enough heat from the outdoor air to properly warm your home. The auxiliary heat is an essential function for maintaining optimal home comfort.

1. The defrost sensor, which is usually mounted on a tube of the condenser, must be closed. The sensor closes when the coil temperature is cold enough to frost or freeze. Once closed, the control board begins saving accumulated run time of the compressor.

4. The system is now in defrost. The condenser heats up quickly because the condenser fan motor is off, melting the frost. The electric strip heat tempers the air that is being cooled by the evaporator.

5. Defrost will continue until the defrost sensor opens. This tells the defrost control, that the coil is warm enough and that no frost is present. If, for some reason, the defrost sensor fails or defrost continues for an extended period of time, the defrost control board will terminate the defrost after specific amount of time (About 10 minutes depending on the manufacturer.)

Checking the defrost control board is quite easy once you know how it operates. Remember, the defrost sensor must be closed and the compressor accumulated run time must be greater than the 30, 60 ,90 pin settings on the board. Here are the steps to check the defrost control board.

After retiring from the U.S. Marines and achieving his B.S. degree, Ron Walker entered the HVAC field. He has been an HVAC technician, service manager, and business owner. Working as a service manager, he spent many years training HVAC technicians to be more technically competent and really understand their trade. His passion for teaching and helping others resulted in the creation of HVAC Training Solutions, LLC.

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