Lennox 80UHG4-75A-3 Blower Issue

[Doby45]

I am hoping I can find a little assistance here in regards to me wonderful (when working) Lennox. Here in Georgia we have gone through a roller coaster of temperatures recently and it has had my AC and my heat cycling back and forth.

Here is the issue at hand. The heat has just recently been working and the AC just before that. Now yesterday my wife had the AC on and the compressor and fan outside were just humming along. Later on the wife said it did not feel that cool, so I placed my hand near a vent and by golly nothing was blowing. Then I went up in the attic, where our furnace unit is, and sure enough the fan was not on. So I went down to the thermostat and turned of the request for AC and placed the switch to off. Then I tried to turn the fan on manually and still nothing. While standing at the thermostat I figured I try to see if the heat worked and it would not fire up.
I then powered everything off, breakers, switch by the furnace and removed the upper and lower cover. I checked the tiny fuse that is on the SureLight board and it is good. I also checked to see if there was any voltage in the blower capacitor with my voltage tester. There was nothing.

I would appreciate any help that could possibly be given and I will be more than happy to answer any question someone may have to help resolve the issue. I can also do good quality pictures if needed. Thank you in advance for your time and consideration in this matter.

[Doby45]

Just for info, I ordered a new fan motor and new capacitor and should have it here in 2 days. Will let you know if that fixes it..

[HayZee518]

ok, restore power to the unit, then power it down. if the capacitor is good, shorting across it should give a clean sharp spark. Use an insulated screwdriver. don't use the meter it could fry it!. with your meter hopefully an analog meter, set your resistance test to RX1. place the probes across the cap. if it is good it will go upscale then back downscale. reverse the leads and touch the cap again. again it should go upscale then back down. if you get this indication then the cap is good. check your control fuse(s) might be a glass fuse might be a cartridge fuse. your control is 24 volt?? or 120 volt?? - Power up the system and check your input to the control transformer, then the secondary of the transformer. if you can get to the movable pole piece of the fan contactor try pushing it in with something insulated. if the motor is good it will start. if it just hums, a start winding might be shot, or the cap might be open. (if it tested ok as above) then yes the start winding might be at fault.

[Doby45]

Well Mr. HayZee I definitely appreciate your reply. I tried exactly that with the capacitor. I powered the system up and then powered it off. When I placed the screw driver across it did absolutely nothing. So in my assumption, the capacitor is bad. I also went ahead and pulled the motor out and made a little plug in the wall pigtail so that I could test the motor. The motor would hum but would not spin unless I spun it by hand. So I also ordered a new motor. My hope is that replacing those two pieces will get this thing going again.

I looked on the control board at the LEDs with the power on and no demand on the system and the LEDs had a slow synchronized pulse to them so it "should" be in a good to go state. If the capacitor and motor does not fix the issue then I reckon I will have to get some assistance on troubleshooting the board.

Thank you sir for your reply.

[HayZee518]

ok, by what you described, the capacitor is bad. replacing this item will make the motor work. but you said you ordered a new motor. change out the cap and save the new motor as a spare. or return it.

[Doby45]

I will try that before I put the new motor in.. I appreciate your help and I will keep you up to date.

[Doby45]

Welp, I replaced the capacitor and now if I hook the cool air lead directly to power the fan runs like a champ. BUT, if I hook it back to the SureLight board and try to cycle the fan on manually or through the cool or heat cycle it will not run. When I turn the cool and heat off and switch the fan to manual I can hear it clicking like the board is making it's switches but it still does nothing. The heat will not kick on either and it was running just a week ago. Is it possible the board can be reset or would it simply need to be replaced?

[HayZee518]

can you send me a circuit diagram through my email?

[hvacwiz]

You need a new circiut board, There is no repair you can do to the board. To get by, you can wire your fan like you did to the furnace main power. that is if your furace is still working in the heating mode.

[Doby45]

Well I am glad to see that I need a new circuit board, since I ordered one. LOL I am in the process now of wiring up the new circuit board but the wiring is slightly different. The newer board did away with a few of Lennox's older boards, so now I am trying to figure out the last 7 wires. I have a photo of both the old wires that are left and the new wires.

[Doby45]

Got it working. The igniter and inducer wires on the little 4 prong connector were jacked up.