So I'm doing battle again with my furnace. Suburban NT34SP. The unit has worked well for the last 16+ years, well except for that whole motor replacement thing 2 years ago.
We're in bed and I'm thinking that it's starting to get cool in the house. I check the thermostat and it says the temp is 68ยฐ. Not good, as I keep it @ 72ยฐ.
Turning the thermostat off and back on yields only a single click, then silence. No blower.
Doing some online troubleshooting tends to point me in the direction of the board, since I just replaced the motor year before last.
I checked for continuity through the sail switch and the over limit switch, both of witch were fine. So, I ordered the board.
I received my new board and installed it today. Now when the thermostat calls for heat I get a repeated relay clicking. Still no blower. I can spin the blower cage by hand, so I know it's not stuck. I also have spun it manually while trying to start it, in case it has a dead spot. No joy. If I run a hot wire to the motor it runs fine.
I have 12.6 v at the furnace. I found that if I unplug the wire from the board to the blower motor, or if I unplug the ground wire from the motor, I get just the normal one relay click.
If I manually close the sail switch, the relay stops clicking. At this point I normally would start looking at the motor again, but if it spins using a hot wire, why doesn't it work when the board feeds it voltage? (I know the board is giving it voltage at the motor because I checked.)
I'm not a furnace repair man by any means. I'm trying to dope this out with logic, but this dope has hit a wall.
Anybody had anything like this?
