Thermostat Wiring Colors Code [HVAC Wire Color Details] Jul 04, 2008Thermostat Wiring Colors Code - High Performance HVAC Thermostat Terminal Designations. Turn the power off before proceeding! Always follow safety instructions especially with electricity. This should be done at the circuit breaker for both the condenser and the air handler/furnace. Basic Thermostat Wiring Colors - Air Conditioner Systems Basic Thermostat Wiring Colors - Air Conditioner Systems - Always remember when changing a thermostat for a new thermostat to take a photo of the colors and where they go on the old thermostat or get a pencil and paper and write it down. It is better to take a good up close photo of the old thermostat and what terminals the colored wiring are terminated.