Suburban Furnace Problem

dougrainer wrote:
Are you positive that you have the Fan motor wires connected to the correct spades on the new module board? Your model board should have the built in FAN RELAY. When you close the contac wires to start the furnace, the relay on the module board closes and outputs 12 volt positive to the Fan motor. The fan motor starts to run and the sail switch closes and starts the Ignition sequence.
1. You may have the wrong module board. Does the Malfunction happen with the original board installed?
2. You have the motor 12 volt pos wire on the wrong spade of the module board
3. You have lost the ground for the furnace, hence the clicking. Doug

I'm sure they are hooked up to the right terminals. I marked the power wire before old board removal. The wires and the board have different size spade connectors also. It's easy to follow the wires on this unit and see that they are correct.

The board does have the built in relay. That's what's doing the repeated clicking.

With the old board I only had one click from the relay, then nothing. I put the old board back in just as a check and it still gave just the one click.

As far as loosing ground...here's the kicker...if I unplug the ground wire for the motor, the relay clicks once. If I put a hot wire on the + side of the motor, it runs (using the existing ground.)

I have a spade connector inline from the board to the motor (from when I replaced the motor), if I unplug this and call for heat, I see 12.4 v on that wire. When I plug it back in, there is no voltage there and the relay starts clicking.

Suburban discontinued the original part number for this board and the new board is supposed to retrofit all models of furnace and water heaters. I'm wondering if my furnace, being about 18 years old, is somehow not captured in this update. The original part number is 520741 and the new board is 521099.