Payne/Resco GA1AAD Furnace Fan Not Running


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Old 01-01-18, 10:08 AM
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Payne/Resco GA1AAD Furnace Fan Not Running

Trying to troubleshoot a furnace/ac fan not running (http://dms.hvacpartners.com/docs/100...IM-GA1A-07.pdf). Tested the thermostat (runs) which has heat, ac and fan controls. Fan alone setting doesn't turn the fan on. Circuit breakers are fine. Air filters are fine (relatively speaking). The fan can spin freely, so there are no obstructions.

Cycling the power on the unit fires up the burners. But the burners then shut down after a while which I assume is because the fan doesn't start. So I don't think the limit switch or thermostat is the issue.

I also removed and tested the fan motor capacitor (GE z97f5705) with a digital multimeter. In comparing my observations with various videos it seems to be Ok. I have another similar furnace and swapped capacitors on the working unit. However the capacitors are not identical.

I am not sure how to test the heat relay. When I cycle the unit on and off I hear the relay click. But I am not sure if that is a complete indication of it working. Various videos to test with a multimeter don't match what my circuit board looks like.

Ultimately I would like to confirm the relay is good and any other components before taking the motor out. So if anyone can advise how to conclusively test the switch or anything else, I would appreciate it.
 

Last edited by SteveOr; 01-01-18 at 10:25 AM.
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Old 01-01-18, 10:34 AM
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Go to the control board. Try a temporary jumper from R to G. There should be a relay click and the blower should start as soon as that connection is made.

For the most part..... the blower is controlled directly from two relays on the control board. If you have an additional relay that is not the control board..... we'd need to see it. The G terminal energized starts the blower in COOL mode. FAN ON and COOL mode are controlled via the G terminal directly from the stat.

The HEAT (LO) blower terminal is controlled via a timer. 30 seconds to turn on after burner lights and user selectable off times after burner shuts off.

Measuring from COM to LO for 120v in heat mode.
Measuring from COM to HI for 120v in COOL or FAN ON mode.

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Old 01-01-18, 11:21 AM
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A jumper from Red on the relay to Ground gives me nothing. No click, nada. Although my multimeter indicates continuity. I also connected a jumper from Red to L2 on page 10 of the pdf linked above per another video.
 
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Old 01-01-18, 11:24 AM
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Is the diagram I posted NOT of your system ?
Be very careful jumping things to 120vac.

If you want to connect 120vac directly to motor..... unplug the terminals from the board.
 
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Old 01-01-18, 11:26 AM
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Looking at the back of the board I see it is fried at the relay. How would I prevent that from happening after I replace it? I could have just done that now. Not sure as I didn't notice anything. Lesson learned.

Edit-- From the smoke pattern, this board burned up before I touched it as it was oriented differently than when I was screwing with it. Plus I would have noticed such a big burn.
 

Last edited by SteveOr; 01-01-18 at 11:53 AM.
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Old 01-01-18, 01:48 PM
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It was probably fried from crappy soldering connections around the relay.
A properly wired board won't do that.
 
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Old 01-02-18, 08:50 AM
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It had about 26 years of reliable use in an otherwise unheated attic. The other soldered connections are pretty solid as it took me some time to desolder the relay from the board (going to try and test it when I get back home tonight). The burn is where the Heat Fan Relay leads to the Cold Fan Relay as shown in the schematic. Which makes sense why I heard the Cold Fan Relay trip but the fan did not go on.

In my limited research, I've read there can be a number of factors that cause a board to fail besides the nearest component. Among them being various things such as resistors, capacitors and diodes not operating to specification. It was unusually cold as well but nothing the furnace hadn't been through before. Hopefully I can get a decent analysis before the replacement comes as I don't want to fry another.
 
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Old 01-02-18, 10:18 AM
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If it's not a solder connection.... the relay was worn out.
 
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Old 01-06-18, 11:11 AM
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Great success! New control board finally arrived after being misdirected enroute. Fan and furnace now operating like normal.

Testing of failed control board's Hot Fan Relay indicates resistance across the poles while energized. This confirms Pjmax's diagnosis.

Thanks for the help.
 
 

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