Air Conditioner Outdoor Unit Will Not Shut Off

This air conditioner problem can occur on central air conditioning systems or on heat pumps when in cooling mode.

Problem: You are running your air conditioner and even when your system cools to the set temperature, the outdoor unit continues to run and just won’t shut off. The indoor unit may freeze up into a solid block of ice. If you let your system continue to run, the ice may continue to build up all the way to the outdoor unit.  You eventually shut off the outdoor unit by turning off the circuit breaker. This problem may be periodic and not occur all the time.

Causes: There are several things that can cause your air conditioner outdoor unit to continually run.

  1. Stuck contactor in outdoor unit (most common): Over time the contacts can become pitted and worn. They can even weld shut so the outdoor unit can’t turn off. Just like spark plugs in your car, the contactor unit should be replaced every few years as part of your maintenance program on your AC system.
  2. Shorted thermostat cable: The wire can get damaged from a weed-eater / weed-whacker, mice chewing on the cable or some other damage. To check the thermostat cable, disconnect from the thermostat and your system. Check for continuity. With the wires disconnected and separated, you should have no continuity.
  3. Bad thermostat: The thermostat could be sending a signal to the outdoor unit even when it is not supposed to.

Does your system need an air conditioning repair? Contact your local HVAC repair company to have a technician do the repair.