Air Conditioner Thermostat Wiring

thermostat wiring
  • 2-3 hours
  • Intermediate
  • 0-50
What You'll Need
Wire cutter

As with wiring any home thermostat, the air conditioner thermostat has a series of wires which need to be connected in order to ensure that it will work correctly. The extent of this wiring is usually described in the air conditioner thermostat manual, but if you have lost the instructions, or cannot follow them completely, then wiring in your stat can be a bit of a challenge. You could call in a professional, and pay money to have it installed correctly, or you can try to do it yourself, following a few simple instructions to get the best out of your device.

Step 1 - Understanding Your Thermostat

The first thing that you need to learn is how your thermostat works. Electricity is delivered to the stat through transformers, and this is used to power different relays, which control energy traveling to the heating or the AC unit. Power from an AC thermostat travels into the unit, and this signals to the air conditioner that it should start working. As power moves about the thermostat, it is controlled by various wires, which prevent the thermostat from delivering the power indiscriminately to any system. These wires should be either connected to the old thermostat, which you would replace, or they are located inside the AC unit ready to be used.

Step 2 - The Wiring

Inside the air conditioner thermostat, there are a number of metal screws on connections. These screws and connections are called terminals, and are the points at which electric wires from your AC unit are joined to the thermostat. These connections themselves control power within the unit, for example the RC terminal takes power from the air conditioner's transformer, and sends the current to another terminal. This connects to wire in a switch, and depending upon whether the switch is on or off, the wire sends a relay to start the unit, or not.

Step 3 - Wiring the Thermostat

Before you touch the wiring, ensure that the electricity is turned off at the breaker board. Take the wires, and trim the wiring and insulation down. If the wire has been damaged, you may need to cut off enough so that you are working with a pristine piece of wire. Depending upon the color of the wire, connect this to the appropriate terminal. For example, the RC terminal is often linked to a red wire. Connected this to your terminal by unscrewing the screw at the top, until you have enough room to slide the wire underneath. Tighten the screw on the exposed wire, not the insulation, and then check that the wire is not loose in the connection.

Step 4 - Finishing

Once you have connected the wires in this way, screw the thermostat back on to the wall, and turn the electricity back on at the breaker board. Check that the thermostat will turn on the AC unit by programming it. If there is a problem, turn off the electricity again and recheck the wiring until you are satisfied that the thermostat is correctly wired.