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Old 04-03-2013, 02:10 PM   #16
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Troubleshooting pilotless furnace problem


Quote:
Originally Posted by JScotty View Post
The filter will cause a main limit to go out, but usually if that's the case the blower would run all the time.
Explain that a little further- I may not know the technical name for everything yet, but if I keep it to ON-HEAT with the temp increased, the blower will remain on for as long as I allow it, and it outputs cold air. Is that what you mean? If it's set to AUTO-HEAT, it hums for a little while, then turns itself off. No blowing at any point in it's cycle.

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Old 04-03-2013, 02:25 PM   #17
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Troubleshooting pilotless furnace problem


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Originally Posted by CaptainRogers View Post
Explain that a little further- I may not know the technical name for everything yet, but if I keep it to ON-HEAT with the temp increased, the blower will remain on for as long as I allow it, and it outputs cold air. Is that what you mean? If it's set to AUTO-HEAT, it hums for a little while, then turns itself off. No blowing at any point in it's cycle.
When you're setting the thermostat to ON-HEAT you're manually turning the blower on. The ON/AUTO switch is for the blower. In the ON position it should always be blowing air & it sounds like it is. Your main limit turns the burners off & blower on when the furnace gets too hot from a lack of air flow (dirty filter, clogged coil, blower not coming on, etc)

Not changing your filter will slow the air down causing the unit to overheat. If the limit trips repeatedly they are more likely to fail. If your main limit is out usually the blower will run no matter if the fan switch is in AUTO or ON. The fact that your fan shuts down in AUTO tells me the main limit is OK.
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Old 04-03-2013, 02:28 PM   #18
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Troubleshooting pilotless furnace problem


Correct JScotty, the blower only run when set to ON, it will not start on AUTO. Nice to cross one thing off the list.
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Old 04-03-2013, 03:55 PM   #19
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Troubleshooting pilotless furnace problem


Update:
86 ohms at igniter
0 ohms at pressure switch
When the thermostat is turned to AUTO-Heat: The igniter glows orange for about 20 seconds and then goes cools back down. The Inducer turns on right away.

Also: Goodman model: GMP075-3
Getting 1 blink from LCD which means ignition failure
0 volts at gas control valve
.18 volts at connection for igniter when I hear it click and it would be glowing if it were plugged in.

Is my control board not sending the proper current to the igniter? Or am I measuring something incorrectly since I'm also getting a 0 for my gas control?

Last edited by CaptainRogers; 04-03-2013 at 05:31 PM.
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Old 04-03-2013, 05:20 PM   #20
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Troubleshooting pilotless furnace problem


Is your gas supply turned on to the home & furnace? Are the other gas appliances in the house working?

Is the gas valve getting 24 Volts when the igniter is glowing? Usually you'll smell and hear the gas flowing if the valve opens. Occaisionally a dirty burner diffuser will divert the flowing gas away from the igniter.

If you get 24 V and it doesn't release gas to the igniter then the valve is suspect. If you don't get 24 V to the gas valve when the igniter is glowing then the board is the likely problem.

Last edited by how; 04-03-2013 at 05:35 PM.
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Old 04-03-2013, 05:32 PM   #21
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Troubleshooting pilotless furnace problem


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Originally Posted by how View Post
Is your gas supply turned on to the home & furnace? Are the other gas appliances in the house working?

Is the gas valve getting 24 Volts when the igniter is glowing?
Gas works for my hot water heater. 0 volts at gas control valve with igniter glowing. 0 volts for gas control no matter what rest of unit is doing.

Last edited by CaptainRogers; 04-03-2013 at 05:37 PM.
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Old 04-03-2013, 05:36 PM   #22
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Troubleshooting pilotless furnace problem


I believe if you follow both electrical lines from the gas valve, they will both make there way back to the board without going through any safety controls.
If so it's a board problem!

Last edited by how; 04-03-2013 at 05:40 PM.
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Old 04-03-2013, 05:53 PM   #23
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Troubleshooting pilotless furnace problem


Slow down for a second. Goodman GMP. Check the heat exchanger for popped crimp rings. They are known for popping them. if they are popped. Time to replace the furnace. The crimp ring will look some what like a 7/16X1-1/4" washer. If you don't have central A/c, you can look don from the top of the furnace after opening the plenum up.


If you have central A/C or a metal plenum with no way to open it. then remove control board and pull blower. Slide into blower compartment and reach up inside it and feel around on the plate for any rings. There is enough room to get your head part way in, or use a mirror.
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Old 04-03-2013, 05:58 PM   #24
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Troubleshooting pilotless furnace problem


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Originally Posted by beenthere View Post
If you have central A/C or a metal plenum with no way to open it. then remove control board and pull blower. Slide into blower compartment and reach up inside it and feel around on the plate for any rings. There is enough room to get your head part way in, or use a mirror.
Yes I hav Central AC. I'm comfortable checking all these sensors and electrical readings, but I don't think I'm ready to dismantle half of the unit and climbing inside to feel something I don't even know what is.

I think I'll call a service man tomorrow and explain the situation and hope he can bring a control board with him.
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Old 04-03-2013, 06:14 PM   #25
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Troubleshooting pilotless furnace problem


I'd get the service tech to confirm that the exchanger is OK before putting out the cash for a possibly useless board change.

They do have an exchanger history.
He can check it out pretty quickly and show you any exchanger pieces he finds. Stay with him to watch the whole process.

Last edited by how; 04-03-2013 at 06:18 PM.
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Old 04-03-2013, 06:22 PM   #26
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Troubleshooting pilotless furnace problem


What am I/he looking for in a bad exchanger? What does the exchanger do?
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Old 04-03-2013, 06:27 PM   #27
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Troubleshooting pilotless furnace problem


post 23 says what to look for.

The heat exchanger is the internal furnace structure that keeps all the CO going out the vent instead of entering the house and our lungs.
It is not repairable when it cracks, perforates or seperates.

Last edited by how; 04-03-2013 at 06:31 PM.
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Old 04-03-2013, 06:35 PM   #28
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Troubleshooting pilotless furnace problem


Thanks again guys, will keep you updated.
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Old 04-08-2013, 10:49 AM   #29
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Troubleshooting pilotless furnace problem


Update: There was a safety between the board and the gas control valve that wasn't getting power. The new safety is ordered and on it's way. The power source coming from the board did not have a straight shot to the valves power supply, but I wasn't sure what it was so I didn't test that connection.

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