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Outdoor heat pumps

Why is My Heat Pump not Working?

Tim H.Verified

Lead Building Engineer

Residential and Commercial HVAC

5,194 positive ratings
Heat Pumps Often Break Because

1. Unit freezes up in either season

2. Fan dies, keeping heat from being spread

3. Belt breaks, which could contribute to the fan not working

A heat pump, as part of a central heating and cooling system, uses the outside air to both heat a home in winter and cool it in summer. When working properly, it should keep your home at comfortable temperatures year around. It is vital to treat heat pump problems immediately before they turn into bigger, costlier problems.

Heat pump problems

A diagram of a heat pump transferring energy into the house

Heat pumps put out enough warm air to reach the desired temperature; however, the air does not get as hot as the air discharged by oil or gas furnaces. If your heat pump is producing much cooler air than you think it should, check the following problems.

Heat pump freezing up

It is common for a heat pump to accumulate a light coating of frost in cold weather; however, the defrost cycle should kick on periodically to melt ice when it detects excessive ice buildup. While in the defrost mode, a heat pump essentially operates in the cooling mode and allows heat from the refrigerant to melt the ice away. As this is happening, a backup heating cycle kicks in until the ice has melted away and the heat pump is ready to operate as normal again. If your heat pump is still frozen after 30 minutes in the defrost cycle, it is best to contact a professional HVAC technician.

Heat pump blower does not work

A heat pump blower motor (or fan) problem can be caused by the thermostat mounted on the wall or the limit switch located on the pump. The limit switch will shut off the heat pump if the air in the plenum (the box that distributes heated air to the ducts) gets too hot.

If the thermostat fan switch is “ON,” turn it to “OFF” or “AUTO.” If this change has been made and the blower still does not work, the heat pump’s limit switch will need to be adjusted. To fix this, you can follow the instructions in your owner’s manual or call a heat pump repair technician.

Broken belt

A diagram of a typical blower motor
A diagram of a typical blower motor.

The belt may be broken if the blower motor is not forcing air through the vents. Follow these steps to replace the belt:

  1. Turn off all power to unit. Remove the door to the front of the air handler cabinet. Note the number stamped on the belt to get an exact replacement.

  2. Install the belt. Slip the belt onto the motor’s smaller pulley first, then the blower motor pulley. The belt will slip into place when you rotate the blower motor pulley while holding the belt in place.

  3. Give slack. If the belt seems to be too tight or difficult to install using this method, you may need to adjust the motor mount to provide more slack. Tighten the tension once the belt is in place. Check the manufacturer’s specifications for this.

Heat pump cycles incorrectly

A clogged filter or a malfunctioning blower can cause the heat pump to turn on and off too frequently. First, try cleaning or replacing the filter.

For a new thermostat, ensure it is properly calibrated. If the thermostat is not installed in an open area, it may not have enough air to show the correct temperature.

When the room temperature rises or drops lower than the desired temperature, the problem could be the heat anticipator in the thermostat. If this does not fix the problem, get in touch with an experienced HVAC specialist.

Heat pump makes noises

Loose cover panels can often cause rattling noises on a heat pump. If they are loose, go ahead and tighten them. Other noises can come from rattling ductwork or loose parts in the handler.

Most heating ducts are metal, which means that they tend to carry noise from the air handling unit to the rooms in the house. To quiet the sound, you can have a heating contractor install flexible insulation ductwork between the heat pump and ductwork runs.

Thermal expansion or loose metal in the ductwork can cause a pinging or popping sound. If you find the source of the sound, try insulating the ductwork from the hangers with rubber cushions and secure any loose metal to cut down on the noise or stop it entirely.

Heat pump troubleshooting

Your heat pump has several components that could prevent it from working properly. Some of these you can check and fix yourself.  

Check the thermostat

First, make sure the thermostat is on the appropriate setting: cool, warm or emergency heat.

A heat pump thermostat wire

If it is a hard-wired thermostat, check the wires. It is possible that the wires have melted together or one has a short in it, preventing the thermostat and heat pump from working.

Check the heat pump for power

The circuit breakers for the air handler and heat pump may have tripped to protect an electrical overload. Check the main electric panel and all subpanels that supply power to the unit. Turn the tripped circuit breaker OFF then ON again to reset the power. If the breaker continues to trip, there could be a short in the electrical system providing power to the furnace.

If there is no power to the heat pump, turn the switch on and wait for the air handler to engage. The heat pump should be connected to a power switch on the wall near the unit or inside the air handler cabinet.

Check electrical elements

If the above troubleshooting has not fixed the problem, then it could be a tripped circuit breaker or fuse that protects the heating elements located in the air handler cabinet. This is common when the heat pump has electrical elements that provide supplemental heat. It is recommended to contact a heating repair technician if you should need to open the heat pump cabinet to work with electrical parts. This can be dangerous if you are inexperienced.

Troubleshooting an outdoor heat pump

The following are possible causes of an outdoor unit not working.

Outdoor disconnect off

Check to make sure the outdoor disconnect is on. A disconnect is a metal box that sends power to outside unit. Some disconnects have a pull out that can be put in upside down to prevent the unit from starting. Others have internal fuses or circuit breakers. If you feel comfortable, you can check the fuses. Pull these out using a non metallic fuse puller and either check them yourself or have checked at a local hardware store. Also, check the inside breaker for the outside unit.

Condensate pump unplugged and/or safety switch open

If you have a condensate pump with a safety switch, check to see if the pump is full of water. If so, make sure the pump is plugged in and the vinyl tubing is clear. Sometimes the end of the tube outside is plugged with dirt. Condensate pumps can be found just above the floor against the indoor unit.

Bad motor

If the outside unit is making noise, but not heating or cooling, check to see whether the fan is running? If it is not, reach in with a long bladed screwdriver and try to spin the fan blades. If they turn hard, this usually indicates a bad motor.

Outdoor reset button tripped

If your outdoor unit has a “Reset Button,” press it. If you have to press it a second time, there is a problem and a service call will be needed.

Unit “locked out”

Your unit may have a safety device locking it out. Reset it by turning the system off at the thermostat or breaker, then after one minute, turn it on. Wait for up to 10 minutes to see if the outdoor unit starts.

Most problems and repairs you can fix on your own; however, sometimes it is a good idea to seek help from an HVAC professional.

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