Goodman Blower not shutting off

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  #1  
Old 10-20-13, 10:07 PM
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Goodman Blower not shutting off

I have a goodman furnace (GMH95) and the blower will not shut off. Here is some background. I had some vibration in the past, and after getting an "open high limit" alarm and the heat would not turn on I found out that the blower wheel fan blades had come apart. Basically the welds broke and just the center of the fan was spinning and causing my noise and vibration. I replaced the blower fan and my noise is gone and I have heat, but now the fan will not shut off.

I have heat, the thermostat is set to "AUTO". If the thermostat is set to 72 degrees and it drops down below 72 the heat will kick on and run until it reaches 72 degrees, but the blower keeps running and does not turn off. I tested the limit switch and it was tripped, so I reset it (manual button) and it read .3 Kohms on my voltmeter. It read OL on my voltmeter before I reset it. My question is, I think the bad blower fan caused the limit switch to trip. I reset the limit switch and I'm still having the issue. Should I just buy a new limit switch or is something else going on?
 
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Old 10-21-13, 05:43 AM
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The limit switch is self-resetting after the unit cools off. You stated you reset the switch manually. I believe you reset one of the rollout switches. Many times when the limit switch trips several times it will weaken and not be able to reset. The limit switch is usually found around the gas valve above the burner box. You can shut off power to the unit, remove the two wires and check for continuity. It should be closed at room temperature and show continuity. If it is "open" you can try to reset it by shutting off power to the unit and tapping the "disk" with the handle of a screwdriver. This will many times reset it. Then re-check it to see if you get continuity. If so, re-install the limit switch and start furnace. It will need to be replaced because if it stuck once chances are high it will stick again. The limit switch is a very important safety device. The reason it tripped in the first place is because of the issue with the blower. The furnace over-heated and tripped it. Here is a photo of a typical limit switch found in a Goodman furnace.
 
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Old 10-21-13, 07:32 PM
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I called a service tech and he thought it was my termostat because the green wire from the thermostate had power after the set time of 100 seconds. He also found a blue wire on the thermostat that was wrong. My thing is the thermostat has been wired like this for 2 years, why am I having issues now? Could the board get reset to factory when I unplugged it to fix the blower wheel? It is working fine now, so we will wait and see.
Thanks
 
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Old 10-21-13, 09:31 PM
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The set time for blower "off" is set on the control board inside the furnace. If your green wire is staying live it may be a thermostat problem.

I would try removing the green wire from the furnace and see if blower shuts off.
If it does... reconnect it at the furnace and disconnect it from the thermostat.
If it shuts off again then it's the thermostat. Either a malfunction or programming.

If it turns out to be the thermostat.... leave a make and model number and we can check into a programming issue or tell you what to check for.
 
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