blower fan will not shut off


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Old 12-04-09, 12:58 AM
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blower fan will not shut off

Hello & Thanks in advance
I have an older York system, Model # (P2MPD20L08001A) w/mainboard G951ADB/Johnson Controls # 031-01234-000 installed in 1994. Everything seems to be working ok except after it reaches the end of the heating cycle and time to shut down, the flame cuts out and the blower fan should stop after about 50 seconds or a little longer. The blower fan will continue to run and the diagnostic code light will continue to blink, until I unplug the unit, if I don’t unplug the unit the blower fan will run all day and the thermostat will no longer control the system. After I unplug the unit I can plug it right back in and the blower fan will stay off until its ready for the next heating cycle.
The diagnostic indicator reads just like this:

CONTNIOUS LIGHT- REPLACE CONTROL
1 FLASH- LOCKOUT CHECK FURNACE
2 FLASHES- PRESSURE STUCK CLOSE
3 FLASHES-PRESSURE SWITCH STUCK OPEN
4 FLASHES-OPEN LIMIT
5 FLASHES- ROLLOUT OPEN
CONTINUE FLASHES-NO CALL FOR HEAT

I tried several new thermostats and that does not solve this problem.
Is it possible the control board is bad? Or is there something else I can try or check?
 
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Old 12-04-09, 01:35 AM
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Is the light blinking continuously, indicating no call for heat?

If not what is it blinking when the fan fails to shut off?
 
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Old 12-04-09, 01:52 AM
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A good wife can be trained to take a break from massaging your feet to go down and reset the furnace when the house starts to cool off. Have you considered this troubleshooting method?
 
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Old 12-04-09, 02:01 AM
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Unfortunately, I'm not finding a manual on the 031-01234 circuit board you are using.

It's possible the motor fan relay is sticking. You might try tapping on the circuit board a bit when the fan is refusing to shut off to see if a little jogging will cause it to shut off.

Generally speaking, circuit boards are treated like black boxes. If all the proper inputs are supplied to the circuit board, you should get the expected outputs. If you don't, you replace the circuit board.

What you describe doesn't sound normal, which implies a bad circuit board, but I hesitate to suggest that when I can't read the manual on the circuit board to check out the various strange things it might be designed to do.
 
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Old 12-04-09, 03:14 AM
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blinking light-no call for heat

Originally Posted by SeattlePioneer
Is the light blinking continuously, indicating no call for heat?

If not what is it blinking when the fan fails to shut off?
Thanks for responding back,
Example, say its 60 degrees If I set the thermostat to 70 degrees for heat, there are no blinking lights, it goes through the motion, still no blinking light(s), the room and thermostat heats to 70 degrees, the flame cuts out, like it suppose to, and at that same time the flame stops the light blinks continously and the blower fan is running and should run for about 50 seconds or a minute or so.
There's no 1 second pause between blinks for trobleshooting.
It blinks like the turn signal in your car or this mouse cursor.
A continuous flashing indicator states-no call for heat.
 
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Old 12-04-09, 07:37 AM
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Yeah. It pretty much has to be a relay. And it likely is on the board if a modern furnace. Although I'd be sure you have no mysterious little devices on the blower housing, or mounted on sheetmetal above the burner area that have a couple wires going to them (although one such device may be the limit switch).

It is the fact though that if you are able to shut off, then reset the furnace right away, without delay, and the blower then no longer runs when you force a very quick new call for heat, that usually those devices I speak of will still cause the blower to start up instantly when you turn the furnace back on, if stuck. The reason is, - they are heat sensitive. Unlike the ones that are built into a board. Make sure you do not have a separate fan timer board that may be replaceable.
 
 

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