I have a Janitrol GMP075-3 furnace and the blower will constantly run unless I turn the power off to the furnace. I believe the problem is from the blower relay because the a/c turns on and shuts off when commanded. I looked at the circuit board in the furnace and I could not tell where the blower relay was located. Maybe I am completely wrong and the problem may be elsewhere. I disconnected the thermostat to see what would happen when I powered on the furnace and the blower still ran constantly. Please help.

Thanks,
Jimmy

I believe I have located the relay. I found two on the board. They both are manufactured by Potter and Brumfield. One has the part #T9AS5D12-22 , Form C, 20A and the other is part # T9AS1D12-22, Form A, 30A. I am not certain which one it is though.

Are these relays plug-in relays or are they hard wired. If they are hard wired the only thing you can do is replace the circuit board, Most circuit boards have the relays identified some way. If they are a plug-in relay pull one of them out and then power up the unit and see if the fan continues to run, if not then try the other one.
Here is a hint that has gotten me trhough the weekend when I did not have a circuit boart in stock; With the power off use something like the handle of a screw driver and tap lightly on both of the relays, then power up again and see if you have made a difference, if not don't give up on the first try... try this three or four times, sometimes this will unstick the points.

The relay is soldered to the circuit board. I am thinking of taking out the board and unsoldering the relay and installing a new one. Is this a good idea, or could I just wire one inline to the existing relay.

Thanks.

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Originally Posted by jimmygtp13

I have a Janitrol GMP075-3 furnace and the blower will constantly run unless I turn the power off to the furnace. I believe the problem is from the blower relay because the a/c turns on and shuts off when commanded. I looked at the circuit board in the furnace and I could not tell where the blower relay was located. Maybe I am completely wrong and the problem may be elsewhere. I disconnected the thermostat to see what would happen when I powered on the furnace and the blower still ran constantly. Please help.

Thanks,
Jimmy

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Jimmy,

Did you ever get this problem fixed? I have the same model furnace with the same symptoms. Usually, a quick internet search will get me in the right direction, but this problem is proving a little more difficult. Any words of wisdom from your experience would be greatly appreciated.

Thanks,
Jay

Yes, I did resolve this problem. I found a wire that was punctured exiting from my thermostat. I found this about 15" down my wall and I repaired the wire and the problem was corrected. I had a similar problem a few years ago and it turned out to be a switch. It was a vacuum modulator switch if I remember correctly. It had clogged so the tubing could not pass air to activate the switch. I cleaned the hole with a pin and replaced the switch just to be safe and it corrected the problem was fixed. I hope this helps a little.

Jimmy

Jimmy,

Thanks for your reply. I did check the vacuum switch and didn't find anything wrong with it. I haven't done anything to the wall around the thermostat, so didn't see how that could have been damaged. I ended up leaning toward your original suspicion of the relay. Since they are soldered on this model, I ended up replacing the control board. I found one for under $100 on the internet and it works well. The install was a piece of cake done in under 10 minutes.

Hope this thread can help someone else in the future.

Thanks again,
Jay

Similar problemwas fixed by removing the blower limiter, cleaning tapping very lightly and reinstalling. The hard part was finding the limiter even though it was right in front of my face. I had bought a new circuit board and when I was checking to see if the wires would all be the same, the board was marked with to terminals for limiter. I followed the wires this was the hard part because of the rats set of wiring, and found the limiter right above the burners on the front of furnace housing. Hope this helps someone!