Troubleshooting Gas Furnace (Goodman GMS30703ANA)


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Old 01-29-14, 11:43 AM
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Troubleshooting Gas Furnace (Goodman GMS30703ANA)

I am a homeowner with two nearly identical units (both Goodman), one for 1st floor, one for 2nd floor. Both units are about 7 years old.

Our 1st floor unit (3 burners) was intermittently failing to ignite (startup sequence made it to the ignitor glowing hot, then failure). It would work for months at a time, then fail occasionally, then work fine for weeks, then fail repeatedly for a day or two, then work fine for days, then fail continuously. Always the same routine: call for heat, inducer start, ignitor light, no flame.

Because our other unit has identical parts, I started swapping: Pressure switch first. Switch worked fine on the other unit. "New" switch installed into the problem unit, and then the problem on the "bad" unit changed: now it will not even start up the inducer. It gets power to the circuit board (red LED light steady red), I can turn on the house fan, but no startup sequence whatsoever (unlike previously when it failed to generate a flame).

So, what are the possible culprits for the original problem followed by the new problem? Which would be the most likely culprit?

I thought: "circuit board". So I swapped circuit boards between the two units (they were identical). Nothing different on the "bad" side; "good" side works fine with the swapped board.

Then, I thought: maybe the ignitor itself. So I swapped that. Same: works on "good" side; nothing different on the "bad" side.

My next guess would be ground wire (inspected it, and nothing obvious wrong with it). I plan to replace it, just in case, but I am ready to call in reinforcements!

I cannot find my multimeter to test anything; decided just to swap potential problems to see if I could hit pay dirt. I've had enough of that and would appreciate helpful suggestions.
 
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Old 01-30-14, 03:20 AM
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If it does not even start the inducer now, while it did previously, what would make sense to explain that new condition?
 
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Old 01-30-14, 10:27 AM
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Apparently, the new problem was a thermostat issue--I jumpered the R/W terminals at the furnace and it will fire up now (all the way to flame). I will fix that issue, and then see where things stand. Not sure I know what the original problem was--any thoughts?
 
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Old 02-01-14, 10:43 AM
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Took off the R/W jumper at the furnace, and connected the R/W wires prior to the thermostat, and it fired right up. So, I decided to hook up a common (C) wire from the furnace to the thermostat to ensure power to the thermostat. Working fine now.

Still do not know what the original problem was. Any guesses?
 
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Old 02-01-14, 10:53 AM
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Pretty hard to get a handle on the problem. The thermostat only tells the furnace to heat or not. It can't let the furnace partially go thru the cycle and stop it unless it was satisfied by heat. Once the thermostat calls for heat the inducer starts..... so as long as the inducer was running the thermostat was not at issue.

Maybe when you switched boards the thermostat wires weren't tight on the terminals.
 
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Old 02-03-14, 11:07 AM
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Thanks, PJMax. Right, the original problem was probably not the thermostat (unless someone chimes in to explain otherwise). Second problem was something to do with the thermostat (worked at the furnace end of the thermostat wires, and worked at the thermostat end, when I jumped the R/W connection). So, I'm still curious to figure out the original problem, in case it crops back up again at some point. Thanks for helping me think it through.
 
 

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