Gas furnace problems.


  #1  
Old 08-25-08, 11:06 AM
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Gas furnace problems.

I have a Suburban Dynatrail gas furnace in my motorhome. When I tried to turn it on, only the blower would come on, no flame. The blower would stay on until I shut the unit off.
I replaced the high limit switch, the unit came on and worked for three cycles, then only the blower would come on and run until I shut it off. I waited awhile and tried again, it ran for one cycle, and again only the blower would come on.
Should I replace the module board next? Or is something else the problem?
 
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Old 08-26-08, 03:45 AM
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Maybe an intermittent problem in the sail switch?
Mike
 
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Old 08-27-08, 02:28 PM
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If replacing the limit switch got the furn to work for 3 cycles and letting it cool will cause it to work for one cycle, then you need to look for why the limit switch is opening. The high limit switch is a safety device designed to keep the furnace from overheating and it sounds like it is doing its job. check for kinked ducting, obstructed outlets ect. also make sure that the return air is not obstructed.
 
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Old 09-01-08, 10:49 AM
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I replaced the sail switch today and ran the unit through 5 cycles without any problems. The old switch did seem a bit stiff. I'll try it again tonight when it's cooler outside.
There are no obstructions in the system.
 
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Old 09-02-08, 07:20 AM
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Unhappy

Back to square one. I started the unit up early this morning, when I came back to check on it, the blower was running with no flame and would not shut off. This is what it was doing in the first place. When it happens while I'm sleeping, it will run the batterys down and make the MH colder.
What should I try next?
 
  #6  
Old 09-05-08, 01:55 PM
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The board cannot shut down the furnace blower. The t-stat calls for heat and the blower comes on then only after the sail switch closes and power gets through the high limit switch does the board get power and light the fire. So check to see if the board is getting power on the wire that runs through the sail switch and the high limit. If it is you may have a flame sense failure or a problem with the gas supply or valves. You will also want to check the supply power for good ground and proper voltage.
 
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Old 09-05-08, 07:03 PM
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Originally Posted by ChrisinAZ. View Post
Back to square one. I started the unit up early this morning, when I came back to check on it, the blower was running with no flame and would not shut off. This is what it was doing in the first place. When it happens while I'm sleeping, it will run the batterys down and make the MH colder.
What should I try next?
Obviously you are not plugged in somewhere? As per Hapdad, be sure to check your voltage. A blower will run on low voltage, but if it's not turning fast enough it will not trip sail switch, plus some gas valves will not open below 9.5-10 Volts.
What are you doing to re-charge aux batteries?
 
 

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