Thermostat problem Atwood 8525 IV Furnace

That is a snap on cover. Right?. If so, the fact that the unit operates properly when cover is off indicats that something is binding the mechenism while cover is on. The most likely culprit is the back side of the cover is touching the coil spring that senses temperature. As it ciols and uncoils ever so slightly it closes the heater circuit or opens it depending on demand. Check REAL closely the back side of the cover to determine if that is a possibility. It takes very little abrasion to prevent proper movement. If replacement is desired the process is disconnecting/connecting two or three wires matching the connections with the old thermostat. Digital units I cannot comment on as have no knowledge.

ndhardy wrote:
I am ok with replacing it if that's necessary but I am curious if I can use one of the hi speed digital types. The one that is there is analogue (springs and magnets).

No such thing as an "analogue" thermostat - it's bi-metal, nor is a digital version "hi speed", whatever that means. :h But yes, many of us have replaced a bi-metal thermo with a digital version ... in my case I chose this Honeywell RTH5100B thermo because the screen lights up anytime a button is pushed so it's really easy to read the screen display even in the dark.

That Honeywell thermostat is probably a really good choice. I've had good luck with Honeywell over the years.

As Sound guy says, all thermostats operate pretty much the same with a bimetal setup. That's good information if you replace it. There are also some thermostats that require 24V to be present (residential furnace), avoid those.

I'd suggest to observe the fitment of the case to the body of the thermostat. It maybe like chainegang said an the mechanism is binding or it could be your interupting the circuit because a wire is moved or connection loosened. It may be the flexing of the body...unknown. I'm cheap so I would modify the cover to avoid the problem. The heat gun would probably be my first tool.

Good luck with that issue, at least you can operate the furnace to keep warm. Today, it is real cold, here.

I had to replace the original mechanical thermostat in this 1991 rig that has an 8500 furnace. Honeywell tech support said this was their only suitable model (but you can get a digital one to work with some wiring creativity)

https://www.honeywellstore.com/store/products/honeywell-standard-millivolt-heat-manual-thermostat.htm

I got a digital one anyway, and got it to work with some help with the wiring.

http://www.canadiantire.ca/en/pdp/honey-non-programmable-thermostat-0529214p.html#srp

Posted: 11/29/17 11:45am by BFL13

I got that RTH111 thermostat and the wiring instructions made no sense so I called Honeywell and was told this thermostat will not work with my 12v system etc etc. (EDIT--that might have to do with the digital ones having their own batteries, which makes them possible to use anyway)

So I told him other guys use it and they say it works, so where do I attach my two 12v wires--pos and neg? (EDIT they are NOT pos and neg, just one wire that is connected and disconnected with the thermostat as its switch)

He said you can try using just W and R and makes no difference which for pos and neg. He says if it does not work,( EDIT-it did work) it will not fry the thermostat, it just won't work. ( He said the CT53K is the model I should have for this job.)

He said never mind the jumper between R and Rc, just leave it there)

Pretty much any thermostat compatible with a two wire furnace will work with the RV furnace. In such an application, the thermostat is just a fancy switch, connecting the two wires together for heat. This means any digital thermostat with battery power for its controls. There are many available.

BFL13 describes how to connect it up quite well. The R and W codes are somewhat standard on thermostats, along with a few other letters, all of which seem to have been assigned more or less at random.

If you need the thermostat to also control an RV air conditioner, things get a little more complicated...or, in some cases, a lot more complicated. It's still often possible to make the swap.