furnace problem in Sunnybrook

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Oct 15, 2011
I have a Sunnybrook 5th wheel and the furnace just died.  Does not come on.  6mo ago replaced the AC control board.  Both AC and furnace share same thermostat.  When switch is placed in furnace position there is a sound from the AC control relay board which I think is doing what its suppose to do but there is nothing from the furnace.  I cannot hear the ignitor clicking from the furnace which I normally can until the burner is lit.  I check the voltages around the furnace and there is a present 12V which seems to be ok.  Also the limit switch on the blower motor seems to be ok.  Would appreciate any info and what the fault could be as the furnace is completely dead. 
With the thermostat on Gas, if the furnace does not start up (fan) within 10 seconds or so I suspect the tiny relay/switch in the thermostat is shot. Working the switch back and forth might help temporarily.

You can check and see if there is 12V on the W lead towards the furnace. If nothing then remove the thermostat from the wall and find the wiring behind it. As a further test you can connect the 12V directly to the W lead, (temporarily)  as it leaves the thermostat and goes towards the furnace and it should start up.

Makes and models for the furnace and the thermostat would help!!
If the furnace fan doesn't come on and run up to speed, there won't be any attempt to ignite the burner. It sounds as though the t-stat is signalling the AC relay board and the relay board is signalling the furnace itself, so either the signal isn't reaching the furnace or the furnace fan controller is not operating. That could mean a bad fan control or no 12v power to the fan motor.
??? Well First things first, what is the year of your 5th wheel trailer, 2nd the make of the furnace > either it's a Suburban or a Hydroflame or a DuoTherm?
2nd did you check the fuse in the converter/ as well if your furnace is a HydroFlame there is a breaker located on the outside behind the outside panel that might have to be reset, if all that is fine then the next thing to check is the klixon relay> if that is your unit is older than the year 2000 if 2000 or newer the control board would have a built in fan control circuit which is micro processor controlled, one of three things would have to be replaced here
A- the klixon relay
B- The D S I Board > equipped with fan control
C- The fan motor itself if the unit gets allot of use> due to wear on the brushes and the armature.
Now depending on what configuration you have will greatly depend on the year of the 5th wheel and the make of the furnace, I need more info
you can Email me at [email protected]
I look forward to here from you :)
Check out my Furnace Troubleshooting guide in the RV Forum Library. It should help you work through the diagnosis.


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