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HVAC Guru
HVAC Guru, HVAC TECH
Category: HVAC
Satisfied Customers: 14031
Experience:  15yrs in the HVAC industry with certificates and degrees.
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I resently had my Lennox 80UHG3/4-100A-2 furnace cleaned and

Customer Question

Hi I resently had my Lennox 80UHG3/4-100A-2 furnace cleaned and now as soon as the flame comes on it shuts down. The code it is giving me it is "main power polarity reversed". I've cleaned the flame sensor already
Submitted: 1 year ago.
Category: HVAC
Expert:  HVAC Guru replied 1 year ago.

Hello and thanks for using this service, if you have been waiting do not worry or get upset I am just one of the techs on here and I try to get to as many customers as I can and I just picked up your question now.

That code 99.9% of the time means the board is bad. You can check the wiring to the furnace and grounding wires, but if all is good you will need to replace the main control board on it. That would happen a lot on that model.

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING LINK on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks

Customer: replied 1 year ago.
Is there any way to test if the board is shot?
Expert:  HVAC Guru replied 1 year ago.

Check the wiring to the unit and then check the grounds that is really about the only way to test for that code, it is pretty much a death code on that unit. The chip on the board that senses the voltage and polarity goes bad...happens a lot.

Customer: replied 1 year ago.
Where do I find a part number for the board?
Expert:  HVAC Guru replied 1 year ago.

Here is a link to the new updated board.

CLICK HERE

We are on the honor system for our time, all I ask is please rate my service using the STAR RATING LINK on your page before you leave. If you are not happy with the service please let me know before leaving a negative rating. This is the only way I am paid or credited through the site for my time. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks