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Old 10-30-2020, 08:50 PM   #1
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Furnaces Shut Down - No Power to Dometic Thermostat

Hi everybody. Iím looking for troubleshooting tips. I searched this topic but didnít find my issue addressed directly. I left our coach with the generator on and 2 furnaces running. 15 minutes later I returned to find the thermostat display dead and the furnaces off. The generator was still running and the generator breaker wasnít thrown.

I pulled the 7.5 amp HVAC controls fuse and found that it had blown. It blew again immediately after I replaced it. I then turned off the coach power using the battery cut-off switch and replaced the fuse one more time. When I turned the battery switch on the thermostat display came back on very briefly and then the fuse blew again. Iím hoping these diagnostic clues are helpful because unfortunately they donít mean anything to me. All suggestions welcomed.
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Old 10-30-2020, 09:55 PM   #2
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I would start with taking the thermostat off the wall and check the cable connection.
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Old 10-31-2020, 09:16 AM   #3
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That circuit provides 12v up to your Dometic roof units. On my 2005 Mountain Aire, it goes to the front unit and piggy backs to the one in the rear.

I would say you have a short in the wire somewhere or one of the control boards in your rooftop units have failed and is causing the short.
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Old 10-31-2020, 09:45 AM   #4
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Quote:
Originally Posted by bentjm View Post
That circuit provides 12v up to your Dometic roof units. On my 2005 Mountain Aire, it goes to the front unit and piggy backs to the one in the rear.

I would say you have a short in the wire somewhere or one of the control boards in your rooftop units have failed and is causing the short.
Agree^^. Start troubleshooting on the rooftop A/Cs.
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Old 10-31-2020, 09:51 AM   #5
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Since you’re blowing fuses you should read this https://www.irv2.com/forums/f50/how-...se-508437.html to help figure out what type of issue you are facing. It’s interesting reading and might help in troubleshooting.

Also what year and model coach? 2019 Ventana 4369?
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Old 10-31-2020, 02:14 PM   #6
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You could also flip the breakers for your ac units one at a time to see if you can narrow it down to one of the units.

You will have to sacrifice a fuse or two in the process.
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Old 11-01-2020, 05:44 PM   #7
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Thanks. Yes, 2019 4369.
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Old 11-01-2020, 05:55 PM   #8
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Quote:
Originally Posted by R.Wold View Post
Since youíre blowing fuses you should read this https://www.irv2.com/forums/f50/how-...se-508437.html to help figure out what type of issue you are facing. Itís interesting reading and might help in troubleshooting.

Typical air conditioner low voltage wiring...
From DC Fuse Block,
Power goes to FURNACE first,
then branches off to go to the
ceiling locations of each air cond.
Power wires in ceiling then will
connect to control boxes / relay
boxes for air conditioner. Tstat

will then get its power from

there.


Given that your were running
the furnaces, I would start my
search at the furnaces themselves.
What I would look for is the power
wires rubbing against shroud of

furnace and grounding out.


There really isn't a lot to go wrong
within the ceiling assemblies for air
conditioners unless using heat strip
on ducted air conditioner.
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Old 11-01-2020, 06:06 PM   #9
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Update: turned off all 3 AC breakers, turned off inverter and battery cut-off and I nstalled new fuse in HVAC controls slot. Turned on generator, flipped cutoff switch back on and thermostat powered up. Flipped on each AC breaker one by one - no issues. Ran each AC unit independently (on AC) - no problem. Ran two AC units at once - no problem. Ran furnaces independently - no issues. Turned on rear furnace while front furnace was running and both units shut down - HVAC controls fuse blown. This time green light on ACHeat also went out and would not come back on until I manually powered up Oasis unit a few hours later.

Just thought I would share this in case it sounds familiar. It’s off to the dealer for me although I was told my local dealer is almost 60 days out on service appointments. I’m considering an off brand shop at this point.
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Old 11-02-2020, 01:16 AM   #10
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Uh, oh. Game changer just played.
Does your Oasis act like acfurnace? Is it on its own fuse? LP or Diesel? Still blowing fuse when Oasis is straight electric mode?
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ace, dometic, furnace, no power, power, thermostat



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