Thermostat Wiring Problems That Cause Your AC To Malfunction

Posted on: 8 July 2021


Your air conditioner responds to signals from the thermostat to start the sequence that turns your AC on. The thermostat sends signals to the air handler indoors and the condenser outside that it's time to turn on and cool your house.

Thermostats can malfunction, and when they do, the problem could be with the wiring. Here's a look at how a thermostat for an air conditioner is typically wired and what an air conditioning repair technician might need to do for a wiring problem.

How A Thermostat Is Wired

Thermostats differ, so you may need to read the manual or call an air conditioning repair service to figure out the wiring problems with your model. For instance, some thermostats run on batteries and use a common wire, or C wire, for backup power. Some thermostats don't use batteries and rely solely on a C wire, while others don't have a C wire at all.

There are several wires coming from the thermostat that connect to the control board in your air handler. The condenser outdoors has additional wiring that goes from the control board to the contactor inside the condenser. This allows the thermostat to turn on the blower in the air handler, condenser fan, and compressor to create cool air.

Wiring Problems That Cause The AC To Malfunction

The first thing the air conditioning repair technician has to do is troubleshoot the system. They may need to test the thermostat as well as the control board and contactor to determine exactly where the problem is. They can use a multimeter to determine where the drop in power occurs and if the thermostat is at fault.

A common problem is loose wiring. Each wire is held in place with a small screw. If the screw is loose, the wire won't have a good connection and this can cause intermittent problems. The solution for this is simple since the repair technician can tighten the screw so the wire isn't loose. The technician may need to check the wiring connections on the thermostat, control board, and contactor to find the problem.

The thermostat wires are held together with an insulated sleeve and passed through a hole in the wall behind the thermostat. The wiring then goes all the way to the air handler and some of the wiring goes from the air handler to the condenser outside. Since the wiring is behind the wall, it's protected, but it can still be damaged by rodents. Also, where the wiring sleeve enters the air handler, vibrations and rubbing might cause the sleeve to be nicked. If the insulation sleeve around the individual wires is nicked, a wire can short out. The repair technician has to replace the wire or repair it so the bare wire is covered and not rubbing against other wires or equipment.

Reach out to a professional for air conditioning repair services if you think yours has a problem.