Persistent E1 Code on Dometic Thermostat: Wiring, Control Board, or AC Unit?

[Brian McKendry]

Hello fellow campers we have a 2015 MK3735 Montana. I Have a E1 code on my thermostat I installed a new thermostat still E1 code then I had a mobile RV tech replace the circuit board on the main AC still E1 code apparently the living room AC Circuit board controls the bedroom ac and the furnace so I had a tech try to bypass the in camper thermostat and take one on the roof with a short connection to check wire still E1 code. So I’m wondering if the bedroom or the furnace could be sending the E1 code back to the main circuit board living room AC or should I replace the main AC would that fix E1 code but what I’m trying to avoid is replacing an AC and it not being the problem. Also I had another tech check the connections and still had AC E1 code
Any advice would be appreciated
Brian

 

[Carl n Susan]

The Search tool is your friend. A quick Search using the keyword "thermostat E!" returned these previous discussions of the issue and solutions, Thee maybe more using different keywords.

Dometic thermostat E1 code

Our Dometic thermostat (+/- 3” square black box type) in the rear of our 2019 3021RL is throwing the E1 error code. If I am reading correctly, that indicates a communication error which shuts down (yes it did) the unit. Called the local mobile service man we have used here in Oshkosh and he said...

www.montanaowners.com

Thermostate/AC Problem

Simple Dometic thermostat lost "comms" with AC and shows E1 code. Tried to reset by turning off completely, held down the + key, and pressed on/off button for three seconds, still show E1 code. Opened some windows, turned on a couple of fans, and put up with outside 84 degrees for a while...

www.montanaowners.com

Dometic thermostat has no power and AC/Furance quit.

on our 2019 3120rl the bedroom AC works. But the the AC and Furnace on the main level quit working and there is not power. Shows a code of E1 on thermostat, any Ideas?? thanks Snowplow.

www.montanaowners.com

Comfort Control Center 2 Thermostat

Recently my thermostat showed a E1 code. I reset it and the 2 A/Cs worked. This moring it showed the E1 code again. Reset it and now it doesn't work and a Zone 4????? along with Zone 1 are now is showing. Zone button doesn't change anything when I push it. Have no idea what to do. Help

www.montanaowners.com

 

[ChuckS]

If you have the Dometic CCC2 Tstat Zone 1 AC control board is the first item the Tstat finds in the CANBUS loop...

Zone 1 AC controls the AC and the furnace.. another telephone cable runs from Zone 1 AC control box to Zone 2 AC control box ... the TSTAT sees both Zone 1 and Zone 2 AC units... However... if there is an issue with the main telephone line from Tstat to Zone 1 then you will get the E1 error because Tstat cant see zone 1 or zone 2....

This is fairly easy to TS with a multimeter and a long single jumper wire....

NOTE - you cant just swap in any standard telephone cable with RJ11 connectors already installed as the plugs are not wired correctly for the Dometic RV-C CANBUS

If you or the RV Tech did not do a RESET on the Tstat that would be the first thing I would try

Added .. Replacing the Zone 1 AC unit WILL NOT fix your issue

 

[Brian McKendry]

If you have the Dometic CCC2 Tstat Zone 1 AC control board is the first item the Tstat finds in the CANBUS loop...

Zone 1 AC controls the AC and the furnace.. another telephone cable runs from Zone 1 AC control box to Zone 2 AC control box ... the TSTAT sees both Zone 1 and Zone 2 AC units... However... if there is an issue with the main telephone line from Tstat to Zone 1 then you will get the E1 error because Tstat cant see zone 1 or zone 2....

This is fairly easy to TS with a multimeter and a long single jumper wire....

NOTE - you cant just swap in any standard telephone cable with RJ11 connectors already installed as the plugs are not wired correctly for the Dometic RV-C CANBUS

If you or the RV Tech did not do a RESET on the Tstat that would be the first thing I would try

Added .. Replacing the Zone 1 AC unit WILL NOT fix your issue

Thanks I did reset Tstat 1st with no change to E1 I also understand about you can’t just swap out with telephone cable
I have this gut feeling I’m going to start replacing ac units and it’s not going to fix problem as you stated in full caps
Thanks for the advise

 

[danaw]

Same problem here at our last trip in ‘25. I replaced the thermostat, no help. I then bought 17 feet of thermostat wire, wasn’t thinking could have bought 3 feet. Went on top of camper with thermostat and wire and hooked it up as close to the AC as possible. Worked perfect. So I thought it must be the thermostat wire chewed by a mouse and I was not ready to try to fish a new wire. So I quit for the day and chewed on it overnight. Didn’t really have any ideas but to look again. I found one of the thermostat wires the size of a hair( almost) was broken with the insulation still somewhat intact. Cut it- it was oxidized- hooked it all up and it worked. I too was ready to buy a new AC.
Plus my thermostat does NOT have the phone like hook up like many suggested. AND word of advice- pull the thermostat fuse before changing so you don’t accidentally touch across it and have to buy another one. You will never guess how I know.
As a side note, our AC compressor had been running a few seconds- kick off and go again. I suppose it was the wire.

 

[harris71]

I had the same issue a few years ago. Replaced thermostat, wasn't that. Purchased an RJ45/CAT line tester on Amazon for $10. Line was good. Replaced the control board on AC1 and it fixed the problem. Had to replace the AC unit about a year later as it finally quit (it was 11 years old and had been used a lot).