Topic: Dometic thermostat E1 code resolution (Read 698 times) previous topic - next topic

This summer during the hottest  part of August, my Dometic thermostat malfunctioned producing an E1 code.  My Dometic AC unit is only a year old but it was past the warranty period.  An E1 code means the thermostat is not connecting with the control board.  I have a Unity IB 2022 so the board is accessed from the roof.

A Google search will produce a number of postings.  The consensus seems to be that corrosion affects the communication wires which are terminated to the board using a telephone jack RJ11.  The recommendation is to replace the RJ11 plug and clean out any corrosion in the terminal.

My unit started working as soon as the temperatures dropped. Since my unit was new I wasn't sure the control board wasn't the problem.  Dometic indicates that the replacement board is part number 3312022.000.  That part is generally unavailable on internet sites.  I went to my local RV dealer who is a Dometic distributor.  They had one on hand which I purchase.  When I got home, the part number on the board was 3312227.000.  I was about to return it but it turned out to be the same part number in my unit.

I decided to replace the board.  During the install I also re-crimped the RJ11 connectors.  I did not replace them.  The communication wires were short (out of a cover jacket) and I was concerned that I wouldn't get them right.  After some false starts, I have a working system. There are two communication wires.  One goes to the thermostat and the other goes to the furnace.  I mixed them up at first and one of the connectors wasn't seated in the board socket properly.  I goth the E1 code again! It is important to clear that by initializing the thermostat after working topside.  You will need the thermostat operation instructions for that.

I recommend downloading the installation instructions for your unit. You will need them for the switches on the board and the wiring diagrams.  Also the operating instructions for your thermostat.  My unit is a heat pump Model 651816.  I was able to Google and find it on Dometic’s site. The wiring diagram is easier to read than the version on the control board cover.  To access the control board, I had to go on the roof, remover the AC cover, and then remove the cover plate that is over the control board. It was difficult to do because my roof has a full complement of solar. In the end, it was worth  it.  The local mobile tech never returned my calls to set up an appointment.  The local Dometic dealer had reservations available for January.  It’s now September.  So it was a time savings project.

I hope this posting helps others in a similar situation.  There isn't a lot out there on the topic, so I  thought it would be good to get this posting up.