Furnace Problem

[Grey Eagle]

We have a 99 Itasca Suncruiser Class A motorhome with a suburban furnace.  Recently we discovered the furnace does not operate.  The relay's that I have found above the microwave appear fine.  When I turn the thermostat, I can hear a click, but the fan never comes on.  The propane tank is full.  Just wondering if anyone has run into anything like this or has any ideas.

Thanks,

Jerry

 

[Ned]

I would suspect the control board or a bad connection.  If the fan doesn't come on, it's either burned out or not getting power.  The state of the propane supply is irrelevant at this point.

 

[Grey Eagle]

Thanks Ned,

Is the control board located on the furnace itself?  I located the furnace towards the left rear of the motorhome and it looks like you almost have to disassemble the motorhome to get to it. :'(

 

[Ned]

You should be able to access it from the outside of the motorhome.  Remove the outside cover and it should be visible.

 

[rclark]

I recently bought a Pace Arrow MH and when testing the furnace I discovered that the propane detector had to be turned on and working to get the furnace to operate!! Just a thought!!

Randy

 

[Gary RV_Wizard]

When the propane detetctor is shut down, it closes a valve in the propane supply so no LPG appliance would work. But rclark's problem is more fundamental - his furnace won't even try to start. 

If the fan won't come on, the fan interlock (sail switch) will prevent the ignition circuit from engaging and the propane inlet to the furnace from opening. The latter two things occur under the control of the furnace circuit board once it detetcs that the fan is running via the sail switch.  The sail switch does not close becasue the fan isn't running, so nothing further happens.  [The sail switch is a switch with a large paddle that sits in front of the fan - when the fan turns the air pushes the paddle to close the switch, indicating that air is being blown through the heat exchanger to carry away the heat output.]

If a click is heard when the thermostat calls for heat, it sounds to me as though the fan relay has engaged but the fan does not begin to run.  I would check the power for the fan (which the relay switches on) and the fan itself.  Could be as simple as a blown fuse for the fan power supply (if it is separate from the power to the furnace circuit board). Could also be a defective fan relay, but if a firm click is heard it is probably working.  Try jumping 12V power direct to the fan and see if it runs that way.

 

[Grey Eagle]

Many thanks to all!  Is there such a thing as a service manual for motorhomes like there used to be for cars?

 

[Tom]

Bob Livingston's RV Repair & Maintenance Manual is worth having around. The chassis stuff will be unique and you should be able to buy a maintenance manual for it. The appliances and other systems are more generic (e.g. most RV manufacturers use the same appliances), so Bob Livingston's manual will apply to many RVs.