lennox g24m3/4-100 gas furnace

[steviey]

furnace died. sometimes it will relight, but goes off aprox 30 seconds later

[hvacdrd]

Can you be a little more specific? Pull off the front panel & observe the burners thru a cycle. Normal operation is...

Combustion blower starts(upper left of compartment on upflow)

Ignitor glows (located in front of right burner)

Burner fires

Flame stays on if sensed within 5-7 seconds, Ignitor turns off

45-90 seconds later the main blower starts

Where are you at in this sequence? When is it going off? Is there a diagnostic light flashing on the control board? If so what does the diagnostic chart indicate? What does it do after it "relights & goes off?"

[steviey]

i believe i solved it. i pulled out the blower motor, all 3 speeds were good, motor capacitor good. i emory papered the flame sensors. i have 110v to the control board, but nothing to the blower motor. also, i forgot to mention before that this all started with a tripped furnace/therostat breaker. the thermostat is working fine. what i found is... the control panel has a burn on the back of it. i will locate a control panel tomorrow and hopefully this is solved. so i dont have to sleep in a snowmobile suit.

[steviey]

not quite fixed yet. i installed the new control panel. the blower fan will not come on.

it is getting the call for heat (from the thermostat). at the control 120v is going in, but at the 3 wires to the blower, it gets 117v(low), 98v (heat), and 63v(cool). is this control panel defective? or is there a sensor or something that may be bad?like i said earlier, i pulled out the blower motor and jumped it with 120v, all 3 speeds work. otherwise with the call for heat the combustion fan goes on, the burners fire up then shut off after about a minute when the blower fan never goes on.

please help.

[hvacdrd]

The voltage at the wires for each speed is a little confusing. Only one of the 3 wires (speeds) will have 120VAC applied at a time. Checking voltage at the other speeds isn't relevant. Check output at the HEAT fan tap on the control after the burner has started. See if you get 120VAC after the time delay (30-60 seconds)

Can you post a picture of the control and how it is wired now? Or do you know the part number?

Is this the control?

[steviey]

yep, thats the one (lennox 19w94). i thought something like that may be the case so i reached in and turned the fan (bird cage) by hand and it started. (kind of thinking that maybe the motor capacitor was going bad, even though i checked it earlier with the ohm meter). but it was making a terrible grinding noise. so i pulled out the motor plus shroud and noticed the motor shaft had about a 1/4" play in and out, and the bird cage is a little out of round. so i backed it off the shaft about a 1/2", put it back together and it works great!

thanks for the input about the voltage ratings on the 3 control plugs. thats good to know if i end up fixing another.