Atwood 7916-II Killing T-Stats

Discussion in 'Heating / Cooling Systems' started by SeaPineMI, Jun 19, 2019.

  1. SeaPineMI

    SeaPineMI New Member

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    I've been searing for weeks trying to find someone else that has had this issue with no luck. Here's a fun one!

    Sorting out our new to us 2006 Fleetwood Sea Pine and the furnace is acting VERY strange. We have a "common" Atwood 7916-II furnace.

    When I first got it, the furnace wouldn't turn on. Took the t-stat apart and noticed the contact wire (what connects the furnace contacts to turn on) was severed (looked burned). Assuming that was the problem, I took the t-stat out, jumped the wires, and voila the furnace ran!

    I ordered a new t-stat and the day I went to install it, tried jumping the wires and nothing happened. Confused, I walked away to get some supplies (volt meter, etc) and when I came back, jumping the wires worked. Figuring I did something wrong the first time, I installed the new t-stat.

    As soon as I flipped on the t-stat...nothing. Jumped the wires and it worked. So I assumed the t-stat was a dud and returned it.

    Bought another and installed it. This one worked great! Problem solved? We were camping this past weekend and the weather was getting down into the 40's at night. Perfect time to try the furnace! Reach down to flick on the t-stat, I hear it click, furnace didn't turn on, and smelled burning electrical. I turned it off, the smell subsided, took apart the t-stat and found the circuit board fried.

    I've traced all the wiring from the furnace to the t-stat and it looks 100% factory untouched. I can't find any evidence of shorts, everything looks perfect. Removing the control board in the furnace is the same, everything looks clean and untouched. No obvious signs of shorts or anything.

    I don't want to start blindly throwing money at the problem. I'm tempted to replace the control board, but at $100+, it's a pricey experiment if it doesn't solve the problem.

    It seems as though there's some sort of voltage controller or something that's intermittently failing in the furnace. I've read a lot about these systems, but haven't found anything about voltage regulation or whatever could be causing the death of t-stats. Seems like the leads that go to the t-stat shouldn't be carrying much voltage, and if there was a short somewhere, wouldn't the furnace just turn itself on instead of killing the t-stat?

    Any ideas?
     
  2. Sjm9911

    Sjm9911 Well-Known Member

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    I would see what the voltage is in the t stat lines. You have something obviously feed it more power then it should have. Trace that back. Im not good with this stuff, but it sounds like its time to get a voltmeter out.
     
  3. SeaPineMI

    SeaPineMI New Member

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    Yea...it's really hard to trace once the t-stat wires route into the furnace housing. I can't really see what they connect to directly. Everything from the furnace housing to the t-stat looks perfectly normal.
     
  4. Anthony Hitchings

    Anthony Hitchings Active Member

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    is it the correct model of T-stat. If it has an "anticipator" wire (with the sliding contact) is that getting fried? Or is your thermostat a fancy electronic one?
     
  5. SeaPineMI

    SeaPineMI New Member

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    The original failed one had the "anticipator" wire...which is what fried. It looked like a factory installation, there was zero scratches or evidence of it ever being taken apart or replaced. The replacements have been cheap digital Honeywell and Emerson heat-only t-stats that I found people have documented success with on here many times.

    The only thing that's weird is the gauge of wire for the t-stat from the furnace...it's massive. T-stat wire is usually 20 gauge or something small, our PUP is running like 12 gauge or thereabouts. The thick wire looked factory in the original t-stat, and it looks factory all the way to the furnace, but who knows?
     
  6. Matt Benoit

    Matt Benoit Well-Known Member

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    Sounds like the thermostats just keep failing because of the electrical. Possibly the voltage is messed up. Or a short somewhere. The furnace gets its 12v from the converter right? Any blown fuses? Maybe the converter is putting out too high of voltage. I would bypass the hidden thermostat wire in the walls of the camper. Get some new thermostat wire and make a jumper at the furnace to rule out a short behind a wall.
     
    Sjm9911 likes this.
  7. SeaPineMI

    SeaPineMI New Member

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    No blown fuses, everything seems to be OK on that front. I was thinking that maybe the converter is putting out too high a voltage, maybe I should check the output. Problem is, the rear of the converter seems to be sealed up, so that would take some level of disassembly.

    The problem with a new jumper wire is figuring out where on the furnace control board the t-stat wires come from. I can trace them into the side of the box, then they route in and it's hard to trace. I'll work harder on it, but the problem seems to be intermittent (hence the first "successful fix"), so I'm not really sure how to isolate that.
     

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