Outdoor Heat Pump Components
© Christian Delbert / Fotolia

Heat pumps are a fairly recent innovation over traditional furnaces and air conditioners. Diagrams make them appear deceptively simple, although they run into problems like any other HVAC unit. Thankfully, many of these issues are easy to repair. The following are some common malfunctions, their possible causes, and the best solutions.

    A Note on Thermostats

    Modern Programmable Thermostat
    © Christian Delbert / Fotolia

    Your thermostat is considered the most likely suspect whenever a technical issue arises, especially in HVAC zoning systems where you have multiple thermostats. Check each thermostat to ensure it is properly set or programmed. You may be having a heat pump thermostat wiring issue. In some cases, especially with modern digital or infrared thermostats, there may be a calibration issue. This latter problem generally requires professional repair due to the complex circuitry involved.

    Common Signs of a Thermostat Problem

    Modern thermostat malfunctions may show one or more of the following issues:

    • The displayed temperature doesn’t match that of a separate, working thermometer.
    • The display shows that it is in heating or cooling mode, but your heat pump is in another mode.
    • The thermostat is indicating the heat pump should be on/off, and the pump has not responded.

    Diagnosing with the Fan Switch

    Some modern digital thermostats include a diagnostics program which shows fault codes indicating the source of a problem. However, the fan switch can also serve as an effective diagnostic tool which any homeowner can use. Simply turning the fan on can answer many questions:

    1. Does the unit have power?
    2. Is the thermostat’s switch functioning and sending the proper voltage?
    3. Is the transformer also relaying the proper voltage?
    4. Is the indoor fan motor and relay functioning properly?

    A working fan can thus eliminate the option of power or thermostat transmission problems quickly. The remaining issues are generally limited to the heat pump itself, making it easier to locate the problem and have it repaired.

    The Fan Isn’t Working

    Chances are, you’ve tried the fan switch test and the fan failed to turn on. You may also have noticed it failing to run when the rest of your unit is functioning properly. This second issue may be accompanied by high electricity bills.

    The Fan Trips Your Breaker

    This symptom points to one of three problems. You may have faulty wiring, the blower motor could be bad, or the control board may need to be replaced. Damage to the motor or control board will require replacing the component.

    The Fan did not Trip Your Breaker

    In cases where the fan simply fails to start during the fan switch test, the fault lies between the thermostat and the fan. This could mean a fault in the thermostat itself, low voltage, or an issue with the fan relay. Contact a certified technician if you are unsure how to test the wires or suspect a thermostat problem.

    When in a Colder Climate

    Many times, heat pumps will have an additional external thermostat when installed in colder climates. When the temperature is below the thermostat’s setpoint, the unit won’t run, even if the indoor thermostat’s settings are triggered. This may generally be fixed by adjusting the outdoor thermostat’s settings.

    My Heat Pump Won’t Start

    This is one of the worst things to discover when there’s a sudden rise or drop in temperature. There are several potential causes, which are easy to diagnose.

    Power Losses

    Occasionally, a heat pump can trip your circuit breaker. However, if it does this frequently, you will want to call a professional in to check for faulty wiring.

    Start Capacitor

    The start capacitor is a component responsible for transmitting an electric charge that starts the motor. You may test the capacitor by simply listening to the heat pump’s cabinet when it’s set to start. A clicking noise is clear evidence the start capacitor needs replaced.

    My Heat Pump Won’t Stop Running

    This issue is not only common, it can lead to damaging your entire system. When in heat mode, a high pressure safety device can shut it off in time. However, when in cool mode, the constant running can cause your indoor coil to freeze. The resulting solid ice builds up and may expand along the pipes to the outdoor unit.

    Compressor Contactor

    This component in your outdoor unit has contacts which become pitted over time and should generally be replaced every few years. Contacts that are not regularly replaced can become damaged to the point where they will fuse together, locking your system into its current mode.

    Short in the Thermostat Cable

    This one’s a little tricky, as shorts sometimes go unnoticed until power stops flowing correctly. In the case of the thermostat cable, the short may be caused by getting nicked by a weed whacker, being pinched too tightly by a staple, or from pests chewing on it. Once diagnosed, this is a simple matter of replacing the damaged cable.

    My Heat Pump Won’t Switch Between Warm and Cool Air

    One of the main qualities that make heat pumps efficient is their ability to provide both warm and cool air by using a reversible heat transfer system. Unfortunately, when something breaks, it can leave your pump locked into one mode. In some cases, you may not even notice an issue until it’s time to change settings.

    Damaged Reversing Valve

    When the heat pump provides cool air but not hot (or vice-versa), your prime suspect is the reversing valve. This valve controls the directional flow of refrigerant, which in turn dictates whether the pump produces warm or cool air. In this scenario, the part must be replaced.

    Refrigerant Leaks

    This issue becomes apparent when the heat pump seems only capable of producing lukewarm air. A refrigerant leak must be handled by a certified technician, who will repair the leak and recharge the amount of refrigerant in your unit.

    My Pump Ices up, Especially in the Winter

    Outdoor Heat Pump Components in Winter
    © onepony / Fotolia

    This problem has two potential causes, some of which will require professional assistance.

    Defrost Controls

    It is possible to manually start the defrost process on your unit. Older and newer models have different methods, but failure of either to start the defrost process will indicate the relevant control component is bad.

    • For older models, manually advance the defrost timer motor until it is set to activate.
    • For newer models, check the electronic defrost control for a set of pins which you may jump to initiate defrost mod. Note that not all modern units have these pins.

    Low Refrigerant

    This problem must be handled by a professional. Another symptom of low refrigerant levels may involve the unit only producing lukewarm air.

    Editorial Contributors
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    Henry Parker

    Henry Parker is a home improvement enthusiast who loves to share his passion and expertise with others. He writes on a variety of topics, such as painting, flooring, windows, and lawn care, to help homeowners make informed decisions and achieve their desired results. Henry strives to write high quality guides and reviews that are easy to understand and practical to follow. Whether you are looking for the best electric riding lawn mower, the easiest way to remove paint from flooring, or the signs of a bad tile job, Henry has you covered with his insightful and honest articles. Henry lives in Florida with his wife and two kids, and enjoys spending his free time on DIY projects around the house. You can find some of his work on Today’s Homeowner, where he is a regular contributor.

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