I have a 1998 Prowler with a Atwood 8535 III furnace that is giving me
trouble.
When I first get to the campground,  I set the thermostat on AUTO and
temperature at a high enough temperature, and nothing happens - no fan
- no burner (of course).  Other times the furnace comes on just fine.

Then if the furnace does come on, when the room temperature reaches
full warmth,  the gas burner will kick off, and the fan will stop a
short time later.  This is normal of course, but sometimes the fan
will not kick off - even if I then set the thermostat to 'off'.  In
those cases I have to pull the fuse to get the fan to shut off.

This is where I stand::

1) I think there is no problem with the gas part - the burner will
always fire up if the fan comes on first.  And the burner will always
shut off properly.

2) The thermostat has three wires going to the furnace -
   Ground
  +12V always
  +12V when heat is set on auto

3) Even though I thought the thermostat was okay, I still bought a new
one and installed it (Coleman Mach).  Did not make any improvement.

I see there is a relay (?time delay?) hanging on the fan motor.  My
thinking is that it must be bad and/or sticking.

Do you guys out there think replacement will solve my problem?  If so,
can you direct me to a site to buy same?  

My predicament is that my trailer is permanent, and so dealer service
would be prohibitive whatwith a 100-mile trip one-way and all.  I
could pull the furnace out and deliver it to the dealer, but he has
already said it will cost at least $250 plus driving charge.  Wow!
The dealer does not have (or says he doesn't) a relay and would have
to 'order' it.

Well that's it!  I await any words of wisdom.  

Geezer