Blower problem, frozen fingers


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Old 11-04-19, 12:12 AM
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Red face Blower problem, frozen fingers

Hello. My fingers are cold from no heat and I type very slow, apologies for making this quick.

PROBLEM:
Furnace goes through cycle and flames ignite, blower refuses to come on. Shutoff for some time, cycles again. I don't have A/C. Note that a few days before this started I had to unclog the tube going from the inducer to the switch. I have since cleaned all the fluedust.


WHAT I'VE DONE:
-Tstat set to AUTO and ON does not start blower. Tstat doesn't control the blower if using heat, right?
-Capacitor is within margins and matches blower requirements. Doubt it's this but didn't hurt to check.
-Checked voltage between CIR-N and HEAT on the board, nothing. Noticed that my meter would flip signs momentarily when flipping the furnace switch on)
-Jumped the blower (R to G) and IT WORKS.


CONCLUSIONS:
Are these signs of a bad control board? It's an American Standard 50A55-486, plan on replacing with a White-Rodgers 50A55-843 https://www.amazon.com/gp/product/B003U4FE8G

Sidenote, I was also told I could just keep the blower jumped. I believe I cannot do this since I have an American Standard board and this would mess with the furnace telling the blower to turn on. Even if I was 99.999% sure I am not going to take the risk of leaving it on.
 

Last edited by DIYPlebian; 11-04-19 at 12:15 AM. Reason: cold
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Old 11-04-19, 02:52 AM
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"-Jumped the blower (R to G) and IT WORKS." Please explain what works.
 
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Old 11-04-19, 04:30 AM
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Blower runs when I switch the furnace on.
 
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Old 11-04-19, 05:25 PM
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Tstat set to AUTO and ON does not start blower.
But it runs when you short R to G ?
That would indicate a thermostat problem.

However..... the blower is timed to turn on in 45 seconds after burner is lit.
The thermostat does not control the blower in heat mode.

If you only get momentary power to the heat blower connection.... that's a bad board.
Remember..... the voltage will not be on the heat terminal until the burner has been on for 45 seconds.
 
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Old 11-04-19, 07:11 PM
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the voltage will not be on the heat terminal until the burner has been on for 45 seconds
Interesting. I will retest the voltage when I put everything back together. I forgot to add I've got a 3 speed motor. Before I gutted this thing I interchanged all the speeds with the cooling and heating terminals. Blower refuses to work in auto and on mode, both cooling and heating (high limit is reached during heating due to inoperable blower).

I have not had the time I wish I had to work on this. When the new board comes in I will report back if it seems to fix this. Thank you for the insight.



Breaking news: my fingers are nice and toasty.
 
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Old 11-18-19, 10:37 PM
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50A55-843 replacement for a 50A55-486 has come in today. Works like a champ.

I've noticed these boards have some sort of transparent substance splotched on the back, presumably to protect the components in one way or another. The old one had part of this substance, about the diameter of a golf ball in size, a deep dark caramel brown. Maybe this was a cause/symptom of the board failing?

Upon further inspection, the discolored portions of the substance were cracked and slightly jutting upwards.
 

Last edited by DIYPlebian; 11-18-19 at 10:58 PM.
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Old 11-19-19, 06:21 PM
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Many boards like that have what is called a conformal coating. It's a thin coating of an epoxy or polymer film to seal the board from moisture and corrosion. With age the coating cracks and becomes unstuck from the board.

Good job. Name:  thumb.jpg
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Size:  1.6 KB Glad you got everything working again.
 
 

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