Goodman GMT115-5 fan randomly turns on


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Old 05-31-17, 06:24 PM
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Goodman GMT115-5 fan randomly turns on

I've seen many similar posts and most point to the fan relay needing replacement; however I'll be darned if I can find this. Could it be built into the control board, which is part number B1809913?

Everything else works fine.

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Last edited by jal2099; 05-31-17 at 06:41 PM. Reason: added pics
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Old 05-31-17, 07:02 PM
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https://www.aircycler.com/pages/aircycler-frv

Do you see an air cycler installed anywhere near the furnace? It looks like a thermostat.

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Do you see any loose or corroded connections to the furnace safety switches?

Does the furnace blink any trouble codes when this issue occurs?
 
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Old 05-31-17, 08:04 PM
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Thank you for your reply. I do not have an air cycler. No trouble codes from the control board, either.

I have not notices any loose or corroded wires. They all seem to be in good shape. Are there any particular color wires i should double check?

Though my thermostat has been in place for a little over a year, I did switch back to the old unit to see if a signal might be coming from the newer unit, but it makes no difference. The switch was only to install a wifi thermostat, which has worked great until this problem.

I'm not opposed to ordering a new control board, which I think is this one, but i'm not exactly keen on dropping $90 to test something. https://www.amazon.com/gp/product/B0...A3ENSQM9L05QCM
 
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Old 05-31-17, 08:15 PM
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I would check the red wire that connects pin 9 and pin 5 to the limit switch.
I would also unplug the 9 pin connector from the control board and inspect for any pins that may have partially popped off.

I have been to a service call after someone replaced a control board to find that the fan would still intermittently run because of a faulty connector to the limit switch.

 
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Old 05-31-17, 08:22 PM
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The blower fan could be turned on if you had a furnace safety open. However if that happened there would usually be a trouble code set.

I would still check for loose intermittent plugs on the control board.
Possibly remove and reseat the large 9 pin one.

The relays for the blower are on the control board. There would be one for heat and one for cool.

I was trying to figure out if that blower was heat activated or timer controlled.
The blower coming on by itself is not a common problem.
 
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Old 05-31-17, 08:57 PM
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Tank you, both. I'll check these all tomorrow. FWIW, the fan does not stay on for any set duration. Sometimes it 3 minutes, other times 15.
 
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Old 06-01-17, 04:39 PM
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those connections seem to be just fine and I don't see any noticeable corrosion or anything out of sorts between pins 5 and 9.

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This is maybe a dumb question, but that switch seems to be more on the "heater" part of the unit, than the a/c part. Am I looking at the correct switch?

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Last edited by PJmax; 06-01-17 at 07:34 PM. Reason: added pic from link
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Old 06-01-17, 07:40 PM
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Did you check the large plug on the control board down below ?

None of the safeties have anything to do with A/C. You have a furnace with A/C added. All those stats monitor over heating conditions when the furnace is running.

One way to let you know the system is in overheat mode is to lock the blower on. So if one of those safeties opened.... the burner wouldn't work and the blower would be on.

Have you checked for trouble codes with the blower running when it shouldn't be ?
You would have to look THRU the blower door sight glass. Once the blower door is opened.... the code is cleared.
 
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Old 06-01-17, 08:05 PM
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Again...THANK YOU for helping me.

I believe so. I've circled the plug i checked in the picture. All the wires and pins are in tact, and are in good shape. This is the plug that has the red wires on 5 and 9 going to and from the limit switch.

And just to be clear (so i'm not miscommunicating), I'm running the cooling not the heater.

I'll double check the blinking light for an error code when the fan is running when it shouldn't, but in the past, it's always been solid red (normal).Name:  IMG_0548.jpg
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And so I'm clear about the terms i'm using...here's a wide pic of the unit i labeled:
The coils are sitting atop this unit, just out of the picture.
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Last edited by jal2099; 06-01-17 at 08:21 PM.
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Old 06-01-17, 08:47 PM
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In an effort to understand things, it seems like the blower would kick on because it things the either "fan on" has been requested or a safety mechanism has been initiated...is that right, or could it be any number of reasons?
 
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Old 06-01-17, 09:00 PM
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Some systems will always monitor for a safety trip but I am not sure if Goodman will. A simple test would be to unplug that safety switch and see if the fan stays on when power is restored. They can be fragile when they get old.


It is probably going to be the board.
 
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Old 06-01-17, 09:18 PM
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Can I just unplug both red wires from the limit switch? If so, will the blower still run? Is the limit switch just for safety?
 
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Old 06-02-17, 12:40 PM
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If I unplug the switch and it stays on, does this mean it's the switch, or does it mean it's something else (the board, I presume).

If I do need to replace the board, would you recommend the OEM board or the updated board? And, if I'm going to be replacing the board, should I go ahead and replace the limit switch?
 
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Old 06-03-17, 08:58 AM
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If you remove a wire from the safety switch and the fan stays on it proves that the switch can cause this issue but it doesn't prove that it is causing it.

ICM boards are cheaper but I don't like them as much. I have installed them with some success but I have had to remove a new one because it was giving a flame sensor lockout at over 2 microAmps DC.

The OEM that I installed gave me a reading of 5 microAmps DC and only required .5 uA DC.
It worked like a champ.

If a limit switch opens you will read 24 volts AC across it (proving potential energy is present)
If a limit is closed you will read 0 volts across it ( because you are basically putting both meter leads on the same side of the load).

I don't actually work on many Goodman or Amana furnaces but I have one on my house.
I see more Carrier, Trane and Lennox gas furnaces than anything else.
 
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Old 06-03-17, 07:47 PM
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So, perhaps good news...the status light was just giving 5 blinks (FALSE FLAME SENSED) to check for a sticking gas valve. Perhaps this is a good place to start.

And to mention it, the draft inducer would turn on sometimes as well.

Is it reasonable to think the board incorrectly believes the heat is on and starts the blower and the draft inducer.

After doing some other reading, other have also come back to the board being the issue. Since I'm in central Texas, I promise the heat is not on. I suppose I could cut off the gas to be sure.

If I do need to replace the valve, is there any reason not to go for the less expensive option:

https://www.amazon.com/Amana-Goodman.../dp/B0024LO4HS

https://www.repairclinic.com/PartDet...7d1443276&mr=1
 
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Old 06-03-17, 07:53 PM
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I would turn off the gas shut off valve near the furnace and disconnect the wire connected to the W terminal. This wire controls the heat function. If the problem persists it is the control board. It is not going to be the gas valve.
 
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Old 06-04-17, 05:23 AM
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I turned off the valve, disconnected the W wire from the control board, and the problem persists. Both the blower and the draft inducer kicked on as soon as I turned the power back on.

Looks like I'll be ordering the OEM control board.

Thank you very much for your help. I'll be sure to follow-up so others will know the resolution.
 
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Old 06-04-17, 07:07 PM
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And to mention it, the draft inducer would turn on sometimes as well.
Well..... that's a biggie to have left out.

The inducer won't start when a safety is open. It certainly looks like a defective control board
 
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Old 06-19-17, 05:24 AM
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I've replaced the board and got the exact same error code immediately. I was careful to replace the board one wire at a time.

Any ideas?
 
 

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