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Old 10-01-2021, 04:16 AM   #1
djac13
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HVAC Dometic Stops running after a minute

I have Dometic DFMD 35121 Medium Furnace Heater in my 2020 cougar. I turn it on and it will run for 1 minute and than turn off and make this high pitch whiney noise for a long time.

The furnace will shut down and then the whiney noise will happen and it happens at the furnace.

I also noticed that on my circuit board, there is a red light that turns on next to the furnace when that alert turns on. Is that fuse bad you think?

I'm guessing it's a shut off warning or something warning you. Just started happening today.

bought the trailer used....
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Old 10-01-2021, 04:48 AM   #2
flybouy
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If you Google Dometic DFMD 35121 you can download the manual.
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Old 10-07-2021, 03:39 AM   #3
djac13
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Yeah flybouy, I’ve done that. It looks like it would be two things, my vents are closed or blocked or a internal circuit board failure.

The vent is easy to figure out. The circuit board failure feels like I need a tech now.
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Old 10-07-2021, 04:51 AM   #4
flybouy
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Do you own a VOM (volt ohm meter) and know how to use it? If not then I'd suggest getting one and learning as they are the most used testing device (other than an air pressure guage) for an owner. Unfortunatly working on the furnace requires removing it from an unfriendly location for most. Be prepared to lay on the floor, arms stretched out and mark/cut the wires and disconnect the gas line and flex ducting. If any of that is beyound your comfort zone (either physically or mechanically) then get a professional.

You may want to check on the mfg date and make sure it's not vovered under Dometic`s warranty. If not I'd suggest replacing the board with a Dinosaur brand. Dinosaurelectronics.com
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Old 10-07-2021, 03:36 PM   #5
djac13
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Yeah, I have a meter. I need a little coaching
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Old 10-07-2021, 05:01 PM   #6
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Sounds like something may be caught in your combustion blower wheel..I’m not up on rv furnaces but I am an hvac contractor..just a thought…I’ve had a bird fly into a home furnace combustion blower and it died..the wheel was spinning against the birds skull and was making a shrill scraping noise..the blower wheel would turn but it wouldn’t engage the pressure switch because of the blockage.
The light on the circuit board should be a diagnostic light..somewhere there should be a chart that tells you what the light codes mean
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Old 10-26-2021, 06:03 PM   #7
djac13
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well, I'm still having this issue and I think I just need a mechanic to look at it to confirm it's a warranty issue with the circuit board. My change is finding that mechanic as I'm traveling around, week to week. I'm currently in the Maryland area and traveling south to florida.
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