How to Properly Wire a Central Air Conditioner Thermostat

Wiring a central A/C is very easy, once you are told how.


Turn breaker of to air handler or central furnace. Even though the voltage is only 24 volts ac, it is always better to work with the power off.

Begin by removing the old thermostat, pulling the cover off and then unscrewing the sub base and removing wires from the thermostat, then remove the thermostat base by removing the screws fastening it to the wall.

Now place the new thermostat against the wall and run the wires through the middle opening of the new thermostat. Fasten the thermostat to the wall with the screws included with the new thermostat, Use a bubble level to make sure the thermostat is level.

Now attach the sub-base to the thermostats base, this is done by placing the sub_base over the mounted base and finding the small screws attached too the sub-base, there are usually three screws.

Now it is time to attach the wires to the sub-base. On the sub-base you will see the letters r,(may have RC and RH) w, g, y, and maybe bl, bk, or, w1, w2, y1, y2. You will not need the later unless you are dealing with a heat pump, if your central A/C is a strait heat/cool A/C you only need the first four. Take the red wire and strip off about 1.4 inch of the wire insulation, back off the screw on the thermostat that is labeled "R" or "RC". make sure there is a jumper wire between RV and RH if your thermostat has these letters, if so then wrap the wire around the screw in a clock wise motion around the R or RC screw. Now screw the head of the screw down firmly making sure the bare end of the wire is not touching any other post. If there is no jumper from the RC and the RH, then you must create a jumper wire, this can be dun by attaching the red wire first to the RC then stripping away a bit of the red wire and placing it under the RH screw and tightening it down. Now take the Yellow wire (if you do not have a yellow wire, that's ok, some thermostat wire uses a blue wire instead of Yellow, just use the blue wire) and strip the end like you did for the red wire and wrap it clockwise around the Y screw and tighten down, Do the same to the white wire to the W screw and the Green wire to the G screw. Now place the cover over the thermostat and turn the breaker on. Your thermostat should now control you central A/C.

Things You Will Need

  • Phillips screw driver
  • Small level
  • Wire strippers


  • There should be a wiring schematic in your new thermostat box.
  • make sure the thermostat you buy is for the kind of unit you have, if your A/C is not a heat pump, then do not buy a thermostat for a heat pump


  • Always Always work with all power off. Never try to wire any electrical device hot.