Question about Goodman GMS90703BXA Heater

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I have a Goodman furnace GMPN080-4 REV B. I had the blower motor take a dive, so I replaced it with another equivalent 115 VAC 60 Hz 1/2 HP motor. I replaced the 10.0 MFD +10% -5% capacitor with a 7.5 MFD +5%-5% capacitor ( Grainger said it was the capacitor for that motor.) I started the furnace and it ran great for 7 days. Great heat and the blower was operating as it should. Then at the end of the 7th day I noticed the blower motor was running but the house felt like it had dipped in temperature. I checked the furnace and I had my status light blinking 4 times (red). The furnace door indicates: 4 BLINKING RED - OPEN LIMIT SWITCH -- AUX LIMIT OPEN/ MAIN LIMIT OPEN. I don't know what to do next. I do know that when ever the furnace was operating as normal, the exhaust (?) fan motor would engage for about a minute or two, then the ignitor would activate, the gas would flame and then within about another 2-3 minutes the blower motor would kick on and I could then check my registers to confirm heat was being sent throughout the house. Now when I set my thermostat to 78 (house is at 68 now) and turn on my power to the furnace it starts the blower motor- but minus the exhaust blower, ignitor, burners flaming,etc. I don.t know where to begin with the Open Limit Switch,... any help?? Thanks.

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  • Anonymous Feb 15, 2009

    I have the same problem where is the switch located, i cant find it

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Limit switch is on the heat exchanger black plastic about 1and1/2 in. by 2 in. with 2 wires going to it , it has 2 screws holding it in take it out and check it with an ohm meter and you should not have a reading if it is good

Posted on Feb 01, 2009

  • bmxbc Jan 12, 2011

    agreed. Sounds like your high level limit. If your fan quit it would heat up causing your limit switch to go. Would save you cracking your manifold. Going through that very thing now. Replaced the blower fan and still had four lights. Turned power off and unplugged both wires and joined them up. Bypassed it and now works fine. Did it for a test only. Trick is trying to replace with the gas line in the way. Anyone know a way around this?

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