Dometic T-Stat has no power

MontanaChef · 01-20-2023, 10:00 AM

Good Day Everyone. We have been full time RV'ers since 2017. Currently live in NW Montana. Most of the problems we have encountered in our Fuzion 429 I've been able to fix. I'm chasing Gremlins now. Last week I noticed the t-stats LED fading and barely readable. The next morning it went dead. No furnace. Nothing. Bought and installed new t-stat (same one) and still nothing. All fuses checked, 13.6 VDC and still nothing. Currently checking all AC units (3 total) and the furnace comm connections. If I am missing something PLEASE let me know. ALL Dealers are 2hrs from us and cannot take in till Spring as we are socked in with the White Gold. Ha!

Any help would be appreciated. Thank you!

**chuckster57** · 01-20-2023, 12:46 PM

Which thermostat?

MontanaChef · 01-20-2023, 12:50 PM

Main inside.

**chuckster57** · 01-20-2023, 12:50 PM

I meant which model.

MontanaChef · 01-20-2023, 12:58 PM

HA! Dometic 10 button black

**chuckster57** · 01-20-2023, 01:09 PM

I’m trying to look in my Dometic training manual for the pin out of the com cable. I haven’t had to troubleshoot your issue so I’m thinking the issue is going to 12V at one of the control boxes in the ceiling unit.

MontanaChef · 01-20-2023, 01:17 PM

I was hoping not but thats what I'm checking today. Haven't tested anything yet with a meter.

MontanaChef · 01-20-2023, 01:43 PM

Just curious....does the In-Command unit underneath have anything to do with it? There is a red light at the BCM power connected indicator D75. ?

**chuckster57** · 01-20-2023, 03:09 PM

Member ChuckS is in my opinion the InCommand Guru, hopefully he will see this and respond. You may want to send him a PM.

ChuckS · 01-20-2023, 08:49 PM

If you Jane the CCC2 Dometic thermostat then the 12 volt dc power to that thermostat comes from the roof Zone 1 A/C control box…

The 12 volts is sent to the roof Zone 1 control box and the Comm cable (telephone cable) plugs into the roof control box and runs down to the thermostat

There are four wires.Red and Black are 12 vdc plus and minus on the end going to thermostat

The other two wires are for the CANBUS signals from thermostat up to all roof mounted A/C units .. they are daisy chained together

NOTE … a standard telephone cable is not wired correctly so you can’t use that to test with

I would get to the Zone 1 AC control box and measure for 12 volts Dc at the control box..if there is no 12 volts present at that control box the thermostat will never work..

You can always temp jumper 12 volts up at that control box to observe if the CCc2 thermostat will now power on..

I’ve added a couple of images to show you where to test for 12 volts at the roof control box (Zone 1)

ChuckS · 01-20-2023, 08:51 PM

Quote:

Originally Posted by MontanaChef

Just curious....does the In-Command unit underneath have anything to do with it? There is a red light at the BCM power connected indicator D75. ?

Since you have wall,mounted thermostat the BCM has nothing to do with your dead display on the thermostat

The red LED on the BCM is just telling you that it is turned ON

ChuckS · 01-20-2023, 08:53 PM

And to make certain … Zone 1 roof AC control box must have 12 volts at its connection or the thermostat will not work ..Zone 1 is the master in the CANBUS loop and the other roof AC units are daisy chained via another telephone cable running to each of the remaining roof AC units

MontanaChef · 01-21-2023, 07:18 AM

Quote:

Originally Posted by chuckster57

Member ChuckS is in my opinion the InCommand Guru, hopefully he will see this and respond. You may want to send him a PM.

Is it safe to say that the Zone 1 control box is the Gremlin in this? Or can it be the other two AC Zone boxes. And would it be faster to just take the CCC2 t-stat and use the comm cable to test each control box? Trying to do a quick bush fix as our outside temps will be bellow 0 this coming weekend and I dont know how quick I can get a new Control box. Or can I take the AC control box from Zone 3 (garage) and swap it out with the main AC 1 in the bedroom (front). And then bypass so the furnace comes on?

Thank you for your quick response. Very much appreciated!

**chuckster57** · 01-21-2023, 07:22 AM

Quote:

Originally Posted by MontanaChef

Is it safe to say that the Zone 1 control box is the Gremlin in this? Or can it be the other two AC Zone boxes. And would it be faster to just take the CCC2 t-stat and use the comm cable to test each control box? Trying to do a quick bush fix as our outside temps will be bellow 0 this coming weekend and I dont know how quick I can get a new Control box. Or can I take the AC control box from Zone 3 (garage) and swap it out with the main AC 1 in the bedroom (front). And then bypass so the furnace comes on?

Thank you for your quick response. Very much appreciated!

Zone 1 control box will be the one that needs 12V to power the thermostat. Zone 1 isn’t necessarily the first or front one. Often times it’s the main cabin one.

With Chucks schematics, it should be easy to test for 12V at the control box, I’m thinking zone 1 is the living/family room.

If you have 12V then you should be able to swap another control box.

MontanaChef · 01-21-2023, 07:24 AM

Quote:

Originally Posted by chuckster57

Zone 1 control box will be the one that needs 12V to power the thermostat. Zone 1 isn’t necessarily the first or front one. Often times it’s the main cabin one.

With Chucks schematics, it should be easy to test for 12V at the control box, I’m thinking zone 1 is the living/family room.

Zone 1 I believe is the front bedroom. That is the only one that has 2 comm cables running from the control box.

**chuckster57** · 01-21-2023, 07:43 AM

Ok, then I would start there.

MontanaChef · 01-21-2023, 07:48 AM

Quote:

Originally Posted by chuckster57

Ok, then I would start there.

Yes thats the plan. But I am wondering if I can swap the Garage AC Control Box (if the front is bad) with the front (Zone 1). And will that turn the T-Stat back on so I can at least use my furnace. Its all about the Heat right now. Or is there another way to bypass to get the furnace on. ?

**chuckster57** · 01-21-2023, 07:54 AM

You need to test for 12V at that control box first. If you need heat is there a store close by you that you can buy some electric heaters?

MontanaChef · 01-21-2023, 07:57 AM

Quote:

Originally Posted by chuckster57

You need to test for 12V at that control box first. If you need heat is there a store close by you that you can buy some electric heaters?

Already have. Okay thanks.

MontanaChef · 01-21-2023, 08:09 AM

Quote:

Originally Posted by ChuckS

If you Jane the CCC2 Dometic thermostat then the 12 volt dc power to that thermostat comes from the roof Zone 1 A/C control box…

The 12 volts is sent to the roof Zone 1 control box and the Comm cable (telephone cable) plugs into the roof control box and runs down to the thermostat

There are four wires.Red and Black are 12 vdc plus and minus on the end going to thermostat

The other two wires are for the CANBUS signals from thermostat up to all roof mounted A/C units .. they are daisy chained together

NOTE … a standard telephone cable is not wired correctly so you can’t use that to test with

I would get to the Zone 1 AC control box and measure for 12 volts Dc at the control box..if there is no 12 volts present at that control box the thermostat will never work..

You can always temp jumper 12 volts up at that control box to observe if the CCc2 thermostat will now power on..

I’ve added a couple of images to show you where to test for 12 volts at the roof control box (Zone 1)

If there is no power going to the Zone 1 AC control box, does that mean the Control box is bad?

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