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Category: HVAC
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Experience:  15yrs in the HVAC industry with certificates and degrees.
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Lennox G40UH-60D-135 furnace. At beginning of winter, one

Customer Question

Lennox G40UH-60D-135 furnace. At beginning of winter, one day furnace would not start when called for heat. Simply removed cover, barely touched wiring harness to inducer and heard relay click on, then heat cycle started up. Unseated plugs and connectors and blew out any dust (very little). No problems for last 3-4 months.Furnace went out again the other day, albeit now with a new thermostat that alerts me of problems (ecobee3).After playing around with connectors again I have come to conclusion that I believe the inducer relay is going bad on the control board. Without rhyme or reason, jostling the connectors on the board manage to get the relay to engage/disengage intermittently. I've taken inducer wiring harness off board and cleaned connectors and adjusted gaps of connectors on the board side to ensure solid connections -- no difference, still intermittent operation.When relay does engage, inducer spins up and furnace goes through normal heat cycle without issue.Need to confirm bad board -- unfortunately at work now and unable to test, looking for suggestions -- have multimeter and am able to test components as necessary.
Submitted: 7 months ago.
Category: HVAC
Expert:  HVAC Guru replied 7 months ago.

Hello and thanks for using this service, if you have been waiting do not worry or get upset. I am APPLIANCE-HVAC GURU a very experienced tech on here and I try to get to as many customers as I can. I just picked up your question now.

Please allow time for me to respond, sometimes I get the questions or responses late so please be patient as I have no control over the site issues. NOTE, I have nothing to do with your payment to the site and did not receive that money.

Check the solder joints byt he relay on the backside of the board for cracking. It is hard to see but with a magnifying glass and a good pair of eyes you can spot it. CLICK HERE....if you see that resolder it and you will be good to go!

The only way I receive any credit at all for my time is by you selecting a STAR USING THE 5 STAR or VOTING RATING SYSTEM AT THE TOP OF YOUR PAGE before you leave for me so please make sure you are rating me not another tech. If you are not happy with the service please let me know before leaving a negative rating. This will also allow you to get directly back to me for FREE follow up questions and tips are greatly appreciated! Thanks GURU

Customer: replied 7 months ago.
Finally had chance to check control board -- looked real hard and did not observe any signs of solder cracking as suggested, however the symptoms sure seemed to line up with that theory real well. For example, if we place the cover on the unit, the slight pressure of the cover against the wire bundle is just enough to make the inducer fan relay to run intermittently. When we take off the cover and rig the cover switch to allow the unit to operate with the cover off, it seems to work fine.I'm leaning in the direction of resoldering those joints just for good measure. Thoughts or other theories?
Expert:  HVAC Guru replied 7 months ago.

Resolder the joints and try it, it cant hurt anything

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