35k Furnace Not Working Properly

**sourdough** · 11-28-2018, 07:48 AM

Throwing this out for comments for a bit since I have to do something pretty quickly.

Got into the 30s last evening and woke up cold a few times during the night with the tstat set at 74 (kept setting it up trying to get warm). Got up this morning and the furnace blower runs non stop while the furnace burner kicks on for about 20 seconds or so then quits. Runs air for about the same amount of time then kicks back in. Putting out "cool" air, not cold - continuous, non stop cycle.

Turned off the tstat and let it sit a minute until everything shut off; turned it back on and the unit kicked in; blower, then the burner kicked in. The burner ran for a longer period and the air got pretty warm coming out of the vents, then the burner shut off and we're back to the same on/off cycle.

I'm thinking the tstat. During the heat spell the last couple of weeks I would find the trailer getting warmer and warmer with the AC on - it just wouldn't come on. Powered down the tstat on those occasions and when turned back on it ran the AC normally. This happened 3 times from Nov. 1. I'm thinking it is getting flaky. I've never had one act up in an RV so just guessing. My other thought would be the control board on the furnace but I don't think these symptoms would be caused by that. Any thoughts/suggestions??

Edit: This is a dometic unit

**sourdough** · 11-28-2018, 10:42 AM

Want to post the resolution in case anyone comes across this problem.

The existing thermostat was a Dometic LCD single zone thermostat, model 3313195.012; a nice little thermostat. We began having issues as I mentioned below. Went across the street (yes it was VERY handy) to get a replacement thermostat. The tstat listed above has been superceded by model 3316250.012. A bit different but just pull the wires/screws off the old and replace them on the new one. Mounting holes are different and the designations for the screws are a big different but pretty self explanatory. Installed the new tstat, initialized it then tested it. Turned on the heater and wow! we're back to the way it used to be - it will run you out and puts out LOTS of hot air. Now, maybe we won't freeze tonite. BTW, one of the installation guides says in red that you must install a new relay box if you upgrade to this tstat. After a visit with the local parts manager he advised this tstat will work fine with the relay from the tstat I had; any others would have required the new relay box so just note that.

66joej · 11-28-2018, 12:14 PM

Thanks Danny. Good info to know.
If only I could remember this when mine craps out.

Tbos · 11-28-2018, 04:43 PM

Good information. Glad you were able to get it fixed quickly.

**sourdough** · 11-29-2018, 03:36 PM

Just want to throw this observation out;

There are lots of posts about AC and furnace issues. My issues came to a head because the furnace seemed to be working but it never put out "heat" and ran continuously, kicking the furnace on for 25-30 seconds and then dropping out for about the same time or a minute. Sounded like it was working - as I got colder and colder over that last nite I kept listening for the furnace burner to kick in and I heard it which made me think everything was OK. It wasn't and no telling how long it had been causing us to run through way too much propane etc. Same with the AC, it ran too much, wouldn't cool like it used to but it sounded like it was operating properly just didn't "seem" like it was operating optimally.

I've now had the new thermostat in for about 32 hours. There is a tremendous difference in how the furnace operates. Instead of coming on every few minutes (finally just stayed on) it comes on very infrequently but keeps the trailer warm. I am anxious to see how it changes the operation of the AC but that may be a few days away.

Took possession of the trailer (new) on 2/26/14 and surprised that a tstat would malfunction so quickly but...… I'm also always amazed at how quickly they make things "obsolete" on a trailer. Went back today and bought a "spare" new thermostat to throw in the closet just because - don't want to have to change out the tstat and the control box next go round.

Just wanted to post these observations in case it might be of some use to anyone having those sorts of issues. It's getting wintertime and we all want our heating to work as well as it can.

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