The colors of thermostat wiring indicate how each is used. To make sure that the thermostat functions properly, you have to make sure that all of the color-coded wires get on the appropriate terminals. While each system can vary, generally, you will find that the wires have universal coding:
- The red wire is the hot side of the transformer.
- The yellow wire deals with the compressor, which typically has to do with cooling.
- The green wire is the furnace blower fan.
- The white wire deals with the heat.