How to Bypass a Dual Fuel Circuit Board to Run the AC

Locate the circuit breaker or fuse box in your home. Open the box and flip the breaker to your air conditioner to the "Off" position. If you are not sure which breaker it is, turn off the home's main breaker. It is typically found in the upper portion of the breaker box.

Shut off the gas at the main valve for your AC if applicable. Find the gas line's shutoff valve at the back of the AC unit. This valve typically has a stubby yellow or red handle. Turn the handle in the gas valve 90 degrees with an adjustable wrench to close the gas valve and shut off the gas.

Locate the power switch next to the AC’s outdoor compressor unit and flip it to the "Off" position.

Take off the screw covers from the top of the air handling unit with a slotted screwdriver then remove the screws behind the covers with a Phillips head screwdriver.

Pull off the top panel to access the inside of the air conditioning unit.

Disconnect any gas lines attached to the unit with a pipe wrench and cap them off. You can also secure these gas lines by applying pipe sealant to the tips of the gas pipes.

Find three colored wires, typically black, white and green, which run between the existing thermostat and the dual fuel circuit board. Disconnect them from the existing thermostat terminal by slightly loosening the screws that hold them in place. Insert these color-coded wires under their designated terminal screws on the new thermostat: black wire to brass-colored terminal screw, white wire to silver-colored terminal screw and green wire to green-colored terminal screw. Tighten down the screws.

Repeat Step 7 to replace and rewire the new circuit board.

Connect the thermostat wires to the air handler's main circuit board. Wrap electrical tape around the wires approximately 4 inches behind the ends of the wires. Tuck these wires behind the circuit board to conceal them.

Reinstall the air handler's cover and screw covers with the appropriate screwdrivers.

Restore power to the system by flipping the circuit breaker to the "On" position. Turn on the gas at the main valve for your AC if applicable. Turn on the AC’s power at the main service panel and allow it to cool the home for at least two hours.