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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 2908
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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I have a Lennox m/n 80UHG3-75A-1 unit in my attic. Installed

Resolved Question:

I have a Lennox m/n 80UHG3-75A-1 unit in my attic. Installed 1998. This month when running in AC mode, the relay(s)on the control board start clicking and the blower motor stops. The unit will continue to click but the motor will not come on. If I shut the unit off and wait 5-10 minutes, the blower will come back on but then again after variable amounts of time, the same thing happens again. Sometimes it take 15 minutes to happen and other times 1 hour but once it starts happening, we usually have to shut the unit off.

Motor or control board failure? Unit appears to work fine in just fan on mode and heating
Submitted: 8 months ago.
Category: HVAC
Expert:  Tim H. replied 8 months ago.

Tim H. :

Please do not rate me until we have finished our dialog and you can rate me as "excellent" service. Thanks for the opportunity to help.

Tim H. :

Hello there.

Customer:

Hello Tim

Tim H. :

Believe it or not, if it only happens in air conditioning, it could be your thermostat.

Tim H. :

Have you tried to run a jumper wire from the R terminal to the G terminal and then turn air on?

Customer:

No I have not tried that

Tim H. :

I would try that first. Turn power off, and then find the board and run a small jumper wire from the red (R) terminal on the board to the G terminal. Then use your air. The fan will run all the time, but we can see if this solves the issue termporarily

Customer:

OK, what would you suggest after that? Issue is sometimes the unit will run for an hour with no problem, other times like tonight, it ran for 15 minutes and then started cutting out. I may have to try a few things tonight and tomorrow

Tim H. :

I suspect the thermostat and that's why I want you to try this. If it still does it after this, then the board would be suspect.

Customer:

OK, I will try that first. I thought the board before the motor as I figured the motor works or it doesn't...Thanks

Tim H. :

Yeah, I would not suspect the motor at this point. However, a thermostat is usually cheaper than a new board.

Customer:

Agreed. I will try this tonight and and see what happens. I assume if all goes well, I will need to replace the thermostat? Also, can I put the jumper at the thermostat screw terminals or the control board in the unit?

Tim H. :

I would put the jumper right on the board across the R-G terminals. Now, remember to turn power off first. Then when you turn on, the blower should run continuously. But I want to see if this still occurs when you use your A/C. If not, I would try a different thermostat and see if that cures it. If it still does this, then you have a bad board. These intermittent problems are the worst kind to try and diagnose.

Customer:

Thanks, XXXXX XXXXX try this. Since I am new to this, is there anyway I can let you know how I make out?

Tim H. :

Yes, definitely keep me posted. You can bookmark the page and always come back to it.

Customer:

Great Thanks!

Tim H. :

No problem

Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 2908
Experience: Experienced in all aspects of HVAC, both residential and commercial.
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