How do you replace the computer board of a gas furnace?

Answer 1

If at all possible, one wire at a time.

After more than one gut-wrenching experience where this 34-year veteran of the trade has lost track of what wire goes where, I can't stress enough that you need to know where each wire goes.


Here's the more detailed procedure.
1. Shut off power to the furnace, and use a "volt stick" to confirm that you're safe to touch the wiring.
2. Draw a map of the existing circuit board and, for each single wire attached to it, identify its color and where it's going. (You don't need to do this if the wires are bundled and attached by multiple plugs, provided those plugs can be distinguished from each other and can only be oriented in one direction.) Use your digital camera or cell phone to provide back-up photos of the wiring.
3. If at all possible, remove only 1 wire at a time. Identify which terminal it was connected to (ie, "R" , "Lo Cool" , "L1" , "N" etc) and mount it on the matching terminal of the replacement board.
4. When all wires have been disconnected from the old board, remove it from the furnace.
5. Physically mount the new board.
6. Turn on the power, and "keep the smoke inside."


The HVAC Veteran