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Heat Pump Outside Unit Not Running? Easy Troubleshoot Guide

If you have a heat pump system that provides both heating and cooling, you have probably seen your fair share of technical challenges and fixes. With winter starting to really take hold, what do you do when your outside unit stops working? You should always contact a qualified technician at Acme AC,1 but there are several common problems you can diagnose and repair. This can save you time, money and some comfort.

There are many reasons why your heat pump will stop working:

  • The thermostat not sending the signal to heat or cool.
  • Power related problems
  • The heat pump is in defrost while in heating mode.
  • The thermostat is in emergency heat mode

Check your thermostat settings and then adjust it to 5 degrees above the current room temperature. Wait for 5 – 10 minutes and check the vents. If warm air is blowing out of the vent, then it is likely that the thermostat is okay. However, if it is not, then it might be time for a new thermostat

Power Related Problems

Power outages and surges happen. One of the most common problems is blown fuses or flipped circuit breakers. If your unit is not working, make sure to check your fuses and circuit breakers. It could be as easy as a flip of a switch.

The Heat Pump is in Defrost While in Heating Mode

During winter, your unit will most likely have a frosting of ice on it. This is normal and nothing to be concerned with. However, if temperatures get really low and there is precipitation, either freezing rain or snow the unit may become encrusted in ice. This insulates the refrigerant from the outside air and makes it very hard for the unit to exchange heat. The unit has a defrost mode but it can lead to a confused state while it tries to exchange cooled refrigerant. This state can damage the unit beyond repair.

To fix this:

  • Melt the ice using water from a hose; do not try to chip the ice using a hard or sharp object because it may damage the coils.
  • Unclog the unit by removing snow and debris.

The Thermostat is in Emergency Heat Mode

When the thermostat is in this mode, it shuts down both the refrigeration system and electric heating elements, which leads to the shutting down of the outdoor fan motor. To fix this, reset the thermostat to normal operation.


This guide is not a substitute for routine maintenance on your system. You should have our professionals at Acme AC handle all your maintenance with our HVAC membership plans.2