I have recently purchase a home and I found two thermostats installed, they told me one controls de AC and heat and the other one heat only, Theyre located on diferent rooms. Can anybody tell me how can I replace this two thermostats into one? thanks

labman

Choose the better located thermostat and remove it from the wall. If you have at least 4 wires, connect them as above. Go to the furnace and connect the yellow, green, and white wires from the thermostat you plan to keep to the Y, G, and W at the furnace. Make sure the blue wire going to the outside A/C is connected to the same transformer as the red wire to the thermostat. Disconnect any second transformer and other wires.

If the location you chose doesn't have the 4 wires, you will either have to use the other, or pull new wires. That isn't too bad in an interior wall.

Usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. Most thermostats and furnaces have the contacts labeled R, B or C, W, Y, and G for the corresponding wire colors. It may be wired to have the A/C control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan. Digital or programmable thermostats may need the blue wire connected to them.

quique0016

the thermostat i want to remove is the heat only thermostat and has two wires only, red and white. Can I pull out this wires and hook them up to the other thermostat?

labman

You may or my not be able to pull the wire out. If not, once you have the other thermostat working, just disconnect it, and leave it. The other thermostat should already have a wire from the transformer. You do not want to hook a wire from 2 different transformers to the same terminal unless the transformers are in phase. Determining that is a pain. Easier to figure out how to use one transformer. If the cable to the other thermostat already has a white wire, all you need to do is to connect it to the W terminal at the furnace. If it doesn't have a white or other unused wire, you will need to add one running from the W terminal at the furnace to the W terminal at the thermostat.