Atwood 2450 Furnace Problem in Glendale

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Metalman RVer

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Dec 3, 2016
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We went to fire up our furnace in the Glendale 5er & nothing happened- no fan. Had a service man who does other work for us come out (he does not usually work on RV's) & we thought we pinned it down to the circuit board, (# 34109)?.we purchased another circuit board & he installed it & still does not work. We circumvented the thermostat by hooking the wires together by the furnace......no work either, so it is not the thermostat. When we bump the reset button the fan jogs a bit & stops.  When we slide the thermostat button there is no movement on the fan. If we go around the board & send power directly to the fan it runs just fine. The red light on the circuit board flashed a code 4 times indicating a sail switch problem but it has continuity, so it is not that we believe. No problem with propane supply either. Any ideas of what it may be?  We are running out of ideas!
 

Metalman RVer

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That's correct...??.it had continuity when it was pushed into position manually.  Does the sail switch engage power the gas valve to open it?
 

Metalman RVer

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Dec 3, 2016
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What we cant figure out is why the fan will just jog when we hit the reset button & then nothing.  Perhaps the new board that we installed is defective? As mentioned yesterday when we activate the thermostat it does not move at all, or the same when we touch the thermostat wires together down by the furnace.....nothing then either.
 

Gary RV_Wizard

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Your understanding of how the furnace operates is insufficient, leading you to faulty assumptions. I suggest reading my RVForum Library article on Furnace Troubleshooting at http://www.rvforum.net/miscfiles/Furnace_Trouble-2.pdf

You can't bypass the thermostat by crossing wire at the furnace - the furnace responds only to +12v on the thermostat wire.  That +12v initiates the start-up sequence, which powers the fan. If the fan gets up to adequate speed, the air pushes the sail switch closed and that completes the circuit to the gas burner ignition logic, i.e. opening the gas valve and sparking the DSI igniter.
 

Metalman RVer

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Thankyou for the information on that. I forwarded it on to my tech guy. An update...??..we changed out our rooftop air conditioner on the RV in July I believe it was & at that time we installed a new thermostat as well, a thermostat that works for both cooling & heating.  Turns out we think now that we purchased the wrong thermostat, to match up with our furnace (our tech man called the Atwood hotline today) which should have been a "pulsing" type & I guess ours was not.  It worked fine on cooling, but not heating.  This is all greek to me, but a new correct Atwood thermostat # 38535 is on order & should be in tomorrow at our RV supplier. Our tech guy is really good but does not do RV work, so we are both learning...??..hope this solves it!
 

Gary RV_Wizard

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Many brands and models of RV-specific thermostats exist, but owners often install other (residential model) thermostats as well and I've not heard of any special requirements like that. Most RV furnaces use a simple on/off type thermostat, but the 2540 is a bit different.  The Atwood 2540 is a two-stage furnace, so it may respond to pulse width to select the low vs high heat stage.  I had two of those for 12 years and they ran off an Atwood Comfort Control System thermostat, along with the two heat pumps.


Your repair guy may benefit from having an Atwood Furnace Service Manual. Get a free one at
http://bryantrv.com/docs2/docs/hflamefurn04.pdf
 

Metalman RVer

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Dec 3, 2016
Posts
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Turns out that before we knew that the new thermostat that we installed in the summer when the AC unit was changed out, was the incorrect one, our tech guy installed the new circuit board (last week) & we think the incompatible thermostat burned it out!  After the Dometic 38535 thermostat was installed (last week) it still did not work, so suspecting that we may have caused harm to the board we took it back & they were good enough to exchange it NC, installed the new board today & it all works now.....all good now.  We live & learn!!
 
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