No power to dometic comfort zone thermostat

[jackel1959]

We have a 2010 3455SA Hickory and right now I am not getting anything on the display of the thermostat when I turn it to the "ON" position. It worked fine a couple of days ago, but now nothing. I have attached a picture of the thermostat.

I have done some troubleshooting, but right now am at a stopping point and need some further advice before I take the rig into the shop. Here is what I have done so far:

1. I checked the 12V fuse and 110 circuit breakers and all is well there. I also verified 110 at the rear and front A/C units.

2. I do have a spare thermostat so I swapped them and still nothing.

3. I connected both thermostats directly to the A/C unit with a separate telephone type cable and nothing.

4. There is a 3A fuse on the control board of the rear A/C and it checks good (just realized there is probably one of these on the front unit too that has not been checked).

5. Re-seated and cleaned all of the plugs on the control board.

Right now I am guessing the thermostat is not getting power (12 or 24v) from the control board in the master A/C unit which I think is the rear one because the front is a add on. Everything has worked fine for several years until today and like I said the thermostat powered up fine 2 or 3 days ago. Any advice or suggestions would be greatly appreciated.

Jack

[jcurtis934]

The rj11 cable used iñ the ac units is not telephone cable, but has the wiring order reversed from one end to the other. Communication over this cable is what is known as Canbuss. Does your docs mention how to do a reset of the system?

[rohrmann]

Take a look at the circuit board in the box below the A/C, accessible if you remove the ceiling panel. We had our front A/C stop working several years ago, and I discovered severe corrosion on the board. I ordered a new box, replaced the box, and the system was back working again.



http://www.dyersonline.com/dometic-c...FZBafgodn2wBug

[jcurtis934]

When this happened to me in my previous rv, diesel pusher with this same thermostat, it was due to no power to the control box from my coach 12vdc supply breakers. Good luck.

[jackel1959]

Thanks for all of the replies.......I will be doing some more checking and troubleshooting today.

[jackel1959]

I just wanted to pass along an update on my thermostat issue:

I downloaded the Dometic Comfort Control Troubleshooting guide back in early April and proceeded to follow all the steps and everything checked good. I even swapped the front and rear A/C control box and no joy. The only thing I didn't/couldn't check was the RJ-11 control cable. So after a day of troubleshooting I threw in the towel and made an appointment with a repair shop I have dealt with for several years where I know and trust the folks.

I took the rig to them on Tuesday, 2 May and they called me yesterday to tell me the RJ-11 control cables that go to the thermostat and the front A/C had both been chewed through They will be able to replace them and everything will be up and running fine again.

And now, the rest of the story..........About a week before the thermostat stopped working I found evidence of a critter(s) in the rig. They had gotten into the front W/D closet and the chase the hides the washer drain line in the bedroom. They chewed through the water supply lines for the washer and the ABS drain line for the washer. Fortunately we had installed shutoff valves on those supply lines a while back, otherwise we could have had a serious flood.

I eradicated the varmints and sealed off suspected entrance points with steel wool, but apparently not before they chowed down on the cables. The Tech at the shop said he doesn't know why, but those cables seem to be a favorite delicacy as he has seen several rigs with this problem when there are critters.

We took the rig on a week long outing after the thermostat stopped working and everything else worked fine and no further evidence of the infestation.

We should get the rig back at the end of this week or the beginning of next. I have attached a couple of photos of the damage I could see and I am sure I will get the cables back when I pick up the rig from the shop.

Thanks for all of your replies and responses,
Jack