Our TT (30 amp service) has a Dometic single zone LCD thermostat that will intermittently not operate.

On our most recent trip, we tested the power and plugged into the 30A on the pedestal but when we tried to turn on the A/C, the digital display on the thermostat was faint and flickering and unreadable. We tried the on/off button several times, but we could not cycle through the panel options (A/C, fan, heat).

We had the campground electrician check the pedestal and it was okay. Everything else in our rig seemed to be working properly.

The next morning, we hit the thermostat "on/off" button and thermostat and A/C worked for the rest of the trip.

When we arrived home and plugged into our shore power here, a similar problem occurred: We turned on the thermostat, the A/C initially kicked on (for about 60 seconds) and then shut down. Again, the thermostat screen display was faint, flickering and unreadable.

Pressing the on/off button did not do anything. The display remained faint, flickering and unreadable.

Two days later, we again tried the on/off button on the thermostat and the A/C worked.

We called to make an appointment with the local RV shop, but we were told that if they could not replicate the problem, there was nothing they could do except charge us for the service visit.

We've ordered a replacement for the thermostat, but we're not sure that will help.

Has anyone else had this problem? Any information or ideas as to what might be causing this or what we can do to better diagnose the possible cause will (as usual) be greatly appreciated!

Sounds like you need to replace your thermostate or house batteries are weakining.

Ugh! Batteries. It's (almost) always the batteries, isn't it? Wish I had thought of that. Will
check them today if it stops raining.

Thanks much!

It wasn't the thermostat. Nor was it the batteries (although one cell on one battery was low).

Any other ideas from anyone?

Is anything else in your rig acting up?

I ask, as that is how we finally located an intermittant issue with our fresh/grey/black/LP tank level sensor. (Flickering, barely readable, or just dark).

Our rig is a class A, so the engine battery gets involved with several features of the coach.
Whenever the tank level sensors would flicker/go dark, the step light would not work, and the automatic awning would just barely move.

After 4 years on the road as full timers, we discovered our engine battery does not charge sufficiently while we are hooked to shore power. (We have no inverter.) Coach batteries charge just fine, and would mask the problem.

In hindsight, I should have guessed. Apparently all those devices are linked to the engine battery, for safety purposes?
(Start the engine: the step pulls in & awning rolls up automatically. Have no idea why the fresh/grey/black tank sensors get involved.)

After much professional input, post cleaning, etc., I just know this is a weak link, and keep the battery 'trickle charger' handy.

In my short span of fulltiming, I have learned it IS aways the batteries.

Some thermostats are battery operated which means they have batteries in the thermostat. Is that the kind you have You need to change them occasionally. Dim LCD is indicative of a battery problem

Thanks for the replies. Everything else seems to be working fine except we noticed that the transfer switch makes noise when the inverter is on. (No, we don't try to power the A/C with the inverter.)

We also thought that the flickering/dim display looked like a calculator with a bad battery, so nice that you mentioned that, too. The t-stat doesn't have a battery backup, though.

The flickering stopped when we installed the new thermostat. We were able to read an E1 error code which apparently translates to "Loss of Communication" according to the thermostat paperwork.

We Googled that error code and found numerous RVers with the same error code and lots of advice on things to try to fix it -pressing both arrow buttons at once, resetting all the breakers, ohm check to name just a few. Nothing has worked so far.

Made another appointment with the RV shop to have the electrical system gone over and make sure there's no issue with our batteries, inverter, converter or on-board surge protector. But, the tech again stated that if they can't replicate the problem (it's still intermittent), then their bill is on our dime even though the A/C system is under warranty.

One thing I forgot to mention is that the rooftop A/C (Dometic) was replaced last winter in Florida due to a non-functioning compressor. Doubt that has any bearing in the matter though since the unit had worked after that.

It's so frustrating to not be able to figure this out and fix it ourselves. *sigh*

If your Dometic is like ours, there is a cable that looks like a telephone wire that connects the thermostat to the air conditioner.

First try disconnecting, then reconnecting, that cable at the thermostat, then at the rooftop unit. Also look carefully at the copper wires in each end to make sure they aren't green, i.e., corroded.

A user on another forum recently found that a wire had broken loose from the back of that connector on the control board at the rooftop end.

It sure sounds like a loose or corroded connection.

Let us know what the answer turns out to be.

Same information from me as well. Dave is correct. This can be a problem with the telephone type cable that goes down to a central unit. If someone as you said worked on it that could be the problem. This will give you a bad time if not right. You can shoot cleaner on the open plug and jack, let it dry and plug it back in. The four button units are a pain to start with. New units now use five buttons.

Thank you so much for these replies and encouragement.

Our tstat has only three buttons, not five (see icon). Does that make a difference in what I should be looking for up top?

We really thought we had it fixed today. We re-re-re-checked all of the inside connections and I found one wiggly wire at the thermostat. Tightened that, turned the A/C on and it worked - no error code and no shut down.

It worked fine 'til I put in the newly-cleaned filter and closed the air return grill. We almost immediately got the E1 error, so figured that there must be something loose up in the overhead compartment where the control module is. Something being moved/jostled/pressed when the grill was closed.

Opening it back up, we wiggled around some of the encased wires and found a brown one that looks somewhat like it could be RJ11 phone cord, but it contained only a bundled pair -red and white- not four (two pairs) like a usual phone wire.

Could this be what you're referring to or would it for sure have four wires like phone cord?

The red and the white wires split off into separate female locking connectors. The red one was slightly loose and had a tiny bit of wire exposed at the neck of the connector. I taped up the exposed wire and made ABSOLUTELY SURE it was connected all the way this time and....the A/C worked without error on the thermostat.

We thought it was fixed, but when we disconnected that wire again, with the unit running, the error didn't replicate. So that likely wasn't it?

I've always unplugged from shore power and had the battery brake on or the batteries completely out when checking the connections. Maybe I need to get brave and work with the power on and start unplugging connectors until the error shows up? (I admit, I'm probably too afraid of being electrocuted to death to try this).

On a probably-unrelated note: The G half of G and J re-checked our batteries using a hydrometer this time since they really didn't seem to be holding a charge very well. We previously tested with a voltage meter, and relied on the on-board panel lights and checking the water level.

The hydrometer showed that three cells on each of our Interstate Group 29 batteries were bad. Took those to our local Interstate shop and after a call to the warranty department, the batteries were replaced at no charge since they were only 9 months old and had a 12 month warranty. Glad we re-re-re-checked. Good stuff happens, too.

We didn't get a chance to get up on the roof this afternoon to look at the outside wiring. Next week, I hope. We couldn't get a shop date 'til the week after next.

I know that these posts have been quite lengthy, and for that I apologize. Thanks again for your help!

We're heading for the RV show up in Hershey PA tomorrow. Maybe Gary Bunzer can figure this out

The RJ-11 "phone cord" connector up top was just fine (no corrosion and polarity wasn't reversed). Bummer - that sure would've been convenient to fix.

Talked last week to a tech at the Hershey RV Show who said he's seen two similar issues recently with these low profile Penguin A/C units. He said it's a problem with a resistor and his fix was to remove that and connect to each other the wires that were connected to the resistor. Not sure what this would do to our Dometic warranty.

Anyway, thanks again for all who replied. I must admit defeat, though, and wait to see if our 'local' repair shop can replicate the error and do anything to fix it.

The good news: We got an earlier shop date and are taking it in tomorrow instead of next week.