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Old 09-22-2021, 08:35 AM   #1
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Lost power to thermostat

Hello all. Ok running coach ac and lost power to the thermostat. While checking fuse panel I found out that there is no 12v power going to furnace fuse bank. All other 12v banks are live.. should I be looking for another fuse somewhere between furnace and fuse bank? Thanks for any suggestions. Dave..
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Old 09-22-2021, 09:35 AM   #2
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Join Date: Apr 2011
Location: Powell River, B.C.
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Welcome to iRV2.

Quick answer ; Yes .

Complete answer we will require all your RV info ; and furnace & thermostat make and model .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.
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Old 09-22-2021, 10:07 AM   #3
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I have a 2011 open range H345MPR 5th wheel with a RV comfort, Coleman Mach thermostat and a Atwood Hydro flame furnace., 8900-III-LD series.
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Old 09-23-2021, 07:14 AM   #4
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Location: Boise Valley (SW Idaho)
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It doesn't look like there is any circuit protection for the furnace system once you leave the off/on switch, if you have one.

RV manufacturers are notorious for not accurately documenting their fuse blocks and breaker panels. My first check would be to pull each fuse, one at a time, and check it. If it's good, move on to the next one, until you've checked all of them.

Here's a link to the service manual for your furnace:

I hopefully attached the wiring diagram for your furnace.

Good luck!
Attached Files
File Type: pdf Hydro Flame 8900-III Wiring Diagram.pdf (239.3 KB, 2 views)
Jim & Angie, Boise, ID
2021 Entegra Esteem 27U
2017 GMC Acadia Denali
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Old 09-25-2021, 01:23 PM   #5
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Got it guys! A relay switch on top of the furnace. Wish I could post a picture to help the next guy. Thanks for the valuable input.
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power, thermostat

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