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Old 05-13-2014, 12:53 AM   #1
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Furnace and fan won't stop running

Hey everyone, I have a 01 cardinal 5th wheel and the furnace fan started running with the tstat turned off. The only way I could get it to stop was to pull fuse. I have since replaced limit switch, trd, and circuit board. Still running. Today I went out and the fan on the ceiling unit was running. Tstat was off the only way I could get it to stop was to unplug unit. Does anyone have an idea what the hell is going on. Thanks
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Old 05-13-2014, 01:14 PM   #2
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There is a time delay relay on the heater the runs the fan after the burner stops, until it cools a bit.

Here's a note from the service manual - it mentions time delay relay

When the thermostat has reached its set point and the demand for heat ends, the gas valve will be de-energized and the flame will go out. The post purge period of 90 seconds begins. When it times out, the blower motor output is removed, and the blower stops.

Here's a link for the service manual.
http://rv52.com/wp-content/uploads/2...n-Furnaces.pdf
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Old 05-13-2014, 04:46 PM   #3
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Thanks for reply. I have replaced limit switch, time delay relay and circuit board. Still runs as soon as I put fuse back in and now my a/c can is running as soon as I plug in and tstat is off
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Old 05-13-2014, 04:51 PM   #4
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How about disconnect the thermostat?
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Old 05-13-2014, 05:25 PM   #5
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Quote:
Originally Posted by Coreyfatboy View Post
Thanks for reply. I have replaced limit switch, time delay relay and circuit board. Still runs as soon as I put fuse back in and now my a/c can is running as soon as I plug in and tstat is off

On your wall thermostat change the fan speed from HI or LO to Auto and all will work correctly.
And keep the new parts for spares. or sell them here.
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Old 05-13-2014, 06:56 PM   #6
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I have pulled all the wires out of the thermostat when I was working on furnace. Furnace still ran. I have not tried it since the ceiling unit has been running
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Old 05-13-2014, 07:22 PM   #7
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Fan control is only on and auto. Has another switch for high and low
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Old 05-14-2014, 07:07 PM   #8
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Interesting - the only thing that can run the fan is the circuit board.

I have seen (on a motorhome) a secondary relay on the air conditioning circuit board that controlled the heater. The two control wires from the thermostat went to this board then to the heater. (Long shot but).

Must be a bad circuit board. Unfortunately there are no real test for the circuit board - You have to have the circuit board tester. That's a trip to the dealer which will cost more than a new circuit board.
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Old 05-14-2014, 07:59 PM   #9
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Is this other circuit board in the ceiling ac unit
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Old 05-15-2014, 09:46 AM   #10
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Yes - I discovered this while working on a 2000 Trek motorhome. Don't know if yours might be the same - as you know wiring diagrams are nonexistent.
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