3 Wire Thermostat Wiring Diagram Heat Only A Comprehensive Guide Unscrew the two wires from the terminals. remove the motherboard of the old 2 wire thermostat and put the new 2 wire thermostat in its place. reconnect the red and white wire, tighten down the set screw, and put the control panel back on. test the 2 wire thermostat wiring by turning the furnace on. R or rc wire (power) connected to the r power terminal to power the thermostat. w wire (heat), connected to the heating control. g wire (fan) connected to the fan control to operate a blower in your hvac system. y1 wire (cooling) connected to the y terminal compressor refrigerant system.
Thermostat 3 Wire Diagram Here’s how to wire a thermostat using the color code and, fyi, each terminal’s purpose. attach the red wire to the r terminal (call for heating and or cooling). attach the green wire to the g terminal (fan). attach the white wire to the w terminal (heat). attach the yellow wire to the y terminal (ac). If you have only three wires for a heat only system, you have three options that don't involve running new wires. these are all described in the ecobee documentation. use your wires for r, w, and c. you will no longer have independent fan control. this is a supported solution. 3 wire wiring for cool only system ( air conditioner only) if you have a first stage air conditioner only, your thermostat will typically be connected to 3 wires, g, rc and y. the rc is power for cooling from the transformer , the g is for the fan relay( controls the blower fan and helps circulate the cooled air.). Step 1: turn off the power. before beginning any electrical work, always turn off the power to the hvac system to prevent any accidents. locate the power switch or circuit breaker for the heating system and switch it off. step 2: remove the old thermostat. take off the cover of the old thermostat by gently pulling it off.
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