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American Standard Freedom 90 Gas furnace blow takes a looong time to shut off

American Standard Freedom 90 Gas furnace blow takes a looong time to shut off

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  #1  
Old 11-22-17, 07:20 PM
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Arrow American Standard Freedom 90 Gas furnace blow takes a looong time to shut off

Greetings all,
We've got an American Standard Freedom 90 gas furnace (installed in 1996!)..
Heat works but after reaching temp the blower stays on for a long time (maybe 30-60+ minutes).
I know the "On delay" is adjustable for up to 180 seconds.
I cleaned the flame sensor.
I pulled a wire on the furnace temp sensor switch but the blower stayed on (not sure if it's a NO or NC circuit though).
Filter was recently replaced.
Also, I've recently replaced the thermostat (though that had no effect on the problem).
Thoughts, advice??
 
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Old 11-22-17, 10:25 PM
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Welcome to the forums.

For exact help you'd need to post the full model number that's on an ID tag inside the furnace near the burner.

It sounds like your furnace has timed blower operation.... if that is correct.... the control board may be bad as it is not shutting off at the correct time.
 
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Old 11-23-17, 08:53 AM
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First off - Happy Thanksgiving!

I feel like such a fool - I should have posted the model number in the first post - my apologies.

It is a AUC100C948B3 and serial number L192TF07G.

The controller is a model 50A50-474 (which seems to be fairly common).
I pulled off the lower cover and then held in the safety switch (the "door switch") and the LED was flashing fast (about 3x a second) which should indicate a "call for heat" and not an error code. Moments later the igniter came on and then the burner "lit".
It seems like the burner will produce heat and then once the thermostat reads that the temperature has been reached the burner shuts off and the fan stays on - eventually blowing colder air. The fan will stay on for a long time - when it eventually shuts down (a long time later) then the heat starts up again.
I suspect - as you mentioned - that I'll need a new controller.
 
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Old 11-23-17, 01:45 PM
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Based on that control board.... the auto blower is strictly controlled from the timer section on that board.
 
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Old 11-23-17, 06:42 PM
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Thanks - I'll be ordering a 50A50-474.
Hopefully that'll fix it.
 
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Old 11-29-17, 06:43 AM
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Good news (for me) - replacing the controller fixed it.
Very simple job (except for the dust and spider webs).
Remove old unit, mount new one and move the wires over one-by-one - pay attention to the ones marked "H" (hot) and "N" neutral, that they go to the appropriate positions.
I sourced the replacement controller on ebay - new one for $120 shipped, arrived in 2 days. Amazon had the same one for $20 more.
There was a used on on ebay for about $50 but I figured it wasn't worth the risk for something that hopefully will give us decades of service.
Thanks all for your advice and support.
 
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Old 11-29-17, 06:34 PM
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Thanks for letting us know how you made out.
 
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