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Discussion Starter · #1 ·
The inducer motor on a 13 year old GMNT80 furnace cuts out intermittently after about 10 min of run time. It only falls out for a second, which in turn cuts out the gas valve. then the ignition process starts over, has no problem lighting again, and about 5 minutes later, motor stops again, and goes thru lighting cycle again. Driving me crazy. any suggestions?
 

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Discussion Starter · #4 ·
No flash codes, and it seems that the voltage is dropping out for a split second when I checked the voltage, but my meter ain't no Fluke... The furnace recently had the heat exchanger replaced, and has been acting this way since. I did notice that there is no ground on the inducer motor. I didn't install the heat exchanger, so I don't know if it was grounded before. Since I am unable to contact the tech that did the previous service I don't know if it was that way before, or he neglected to ground it when he put it back together. Is it possible that the lack of a ground is causing the motor to fail?
 

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Discussion Starter · #9 ·
it is a condensing furnace, and both the primary and secondary heat exchangers were recently replaced. would the pressure switch open and close immediately without causing the board to give a fault signal?
 

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Was that stat bypass at the stat or in the furnace? It should be done at
R & W within the furnace to eliminate stat wire or connection issues.

I'd also try temporarily bypassing the door switch just to make sure that isn't the cause of your intermitant power drop out.

If you are getting the furnace ID short cycling without a cause external to the furnace and without the board giving you a fault code then the board is suspect.

Your furnace also has a rep for board ground issues damaging the boards. Check if the plate that the board is attached to is firmly attached to the blower. I'd be checking all your grounds (board/furnace & designated circuit).
 

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1) Unplug and reconnect the white molex plug connectors from the board. Male-female plug connectors as you may have a poor connection. Look at the pins inside them with a magnifying glass as one may be pushed back and not seating.

2) Check the wiring connections at the board

3) Jumper R-W and run it. If it works good then the tstat may be dropping out or flickering

4) Make sure the mount the board sits on is tightly attached to the fan housing and add bigger screws if loose or else it loses ground.

5) Most likely at that age the relay for the inducer is weak and fluttering. Try tap them gently with a screwdriver and if it drops out then it is most likely weak.
 
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