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Old 07-26-2014, 10:07 PM   #1
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Goodman GMT blower runs intermittently


Hi all,

Have 11 yr. old Goodman GMT (or GMTH, can't find data plate). The blower won't run more than a few seconds. Starts and spins up normally, but shuts down right away. If you let the whole thing sit for a few minutes with power off, it might run a little longer, say 30 seconds. Felt the blade, it turns smooth and easy as pie. Motor sounds good / normal when it does run. Looked around briefly and can't see any burnt parts, loose / broken connections or parts, etc., including on the board. I can hear one of those small relays on the board click each time the fan turns on and off, so the relay seems to be working. First time, here, any help appreciated...
(Trying to post pics of unit and diagram, but not sure how to attach more than one pic.)
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Old 07-26-2014, 10:09 PM   #2
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Goodman GMT blower runs intermittently


diagram
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Old 07-26-2014, 10:12 PM   #3
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Goodman GMT blower runs intermittently


You should have a steady 24 volts from Y to C when the AC is on and G to C when the AC is on or the fan in the Run position on the thermostat. If you do and it still cuts out then the board and fan relay may be faulty. 10-11 yrs is average life for some of those relays and boards.

If you do not have steady 24 volts then the thermostat may be faulty.
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Old 07-26-2014, 10:13 PM   #4
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Goodman GMT blower runs intermittently


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Old 07-26-2014, 10:15 PM   #5
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Goodman GMT blower runs intermittently


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Old 07-26-2014, 10:18 PM   #6
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Goodman GMT blower runs intermittently


Also, I checked that round thermal cut-off-looking-thing on the fan housing - it is closed (i.e., zero ohms). On the right in the picture. Not sure what that is about.
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Old 07-26-2014, 10:18 PM   #7
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Goodman GMT blower runs intermittently


There should be a terminal strip where the thermostat wires attach and RWYGC terminals. However on some of the basic Goodmans they connected those wires in the air with wire nuts. Then you have to find those wires and check them live or call a Pro.

That thing is a high temp limit switch in case you have 2 furnaces tied together and one fan stops and belches heat into the other. Not your problem.
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Old 07-28-2014, 06:31 PM   #8
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Goodman GMT blower runs intermittently


Yuri, by C, do you mean a common - what I might call ground, or chassis ground? (Four wire t'stat)
Thanks again
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Old 07-28-2014, 07:39 PM   #9
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Goodman GMT blower runs intermittently


Good ole Goodman basic unit. Actually it works OK but they cut a few corners to make it a builders grade unit. C on them is a wire from the secondary side of the transformer. There are 4 wires on the transformer. Primary ( high voltage ) and Secondary ( low voltage ) which are for your thermostat. They ground the secondary and from what I can see on your pic it is the blue wire with 2 other wires attached to it. The black and white are 110 volts. Blue and orange are 24 and the orange is 24 volts hot. Check from the orange to the chassis to see if it is 24 volts. Then check to the blue and see if it reads 24 volts. The blue should be C and have a wire to the chassis. Would have made it a he*ll of a lot easier if they had put a terminal strip on.
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Old 07-28-2014, 09:32 PM   #10
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Goodman GMT blower runs intermittently


OK, first - I told a fib - the thermostat is actually three wires, but I'm still learning to count. Anyway it doesn't matter, you called it on both accounts. One side of secondary is grounded (Blue), and there is a steady 24 volts Y to C when calling for AC; steady 24 volts G to C when calling for AC or fan run. In both cases, the blower ran for a few seconds then stopped, and in both cases the 24 volts stayed on. Just for giggles I tried another thermostat, same result. So can I get a board for this thing, or do I need one of those pesky license things?

Back in the day we used to actually fix boards of about this complexity, (other stuff, not HVAC) but that doesn't pay off much any more.
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Old 07-28-2014, 09:56 PM   #11
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Goodman GMT blower runs intermittently


guess it depends on how you look at it - fourth tstat wire connects directly to condenser - no connection to air handler.
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Old 07-28-2014, 10:51 PM   #12
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Goodman GMT blower runs intermittently


Buy a new board. Make VERY sure the mounting plate the board attaches to is VERY well secured to the fan housing. If it comes loose you lose grounding and it blows the board. I have had to add a couple sheet metal screw to it as the 2 they use come loose.

Try these guys for the board or americanhvacparts.com
http://www.supplyhouse.com/
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Old 07-30-2014, 09:16 AM   #13
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Goodman GMT blower runs intermittently


So it seems like I found an exact replacement at supplyhouse - ICM280. Ordered it today. I'll be careful on the grounding issue - thanks so much for your help on that - and everything. More news soon...
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Old 07-30-2014, 09:20 AM   #14
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Goodman GMT blower runs intermittently


Yur Welcome
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Old 08-03-2014, 04:01 PM   #15
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Goodman GMT blower runs intermittently


Good news first: the board showed up promptly, came complete, and looks to be an exact match, so a big thank you to SupplyHouse.com.

Now for the bad news. The system does the *exact* same thing as it did with the old board. Blower runs for just a few seconds - usually just 3 or 4 - then shuts down. After maybe 10 cycles of this (tstat calling for fan only), I was looking and feeling around, and the motor is running pretty hot - I can touch it, but not for too long. Measured ~150 degrees, sometimes more. That was after only 10 minutes, and 90% of that was off-time. Total run time couldn't have amounted to more than a minute or so. Seems pretty clear to me that the motor is overheating and the internal thermal protection is working. Thoughts?

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