Another AC question

The opinions and observations below are mine--yours may vary.

Off the road again, and some more time to reply. So, I took a look at my latest remote and sure enough there are 2 nonfunctional, not labeled buttons, for a total of 12. I'll just call it the tstat of many buttons. I did not mean to imply that it could be installed by itself. The Dometic tstats are paired with specific control boards. In fact I am suspicious that the problems with the screwy fan speed switching by the few button remote is more of a control board problem. However, the many button remote and corresponding control board installed in our trailer by a competent AC technician running 1 AC unit does an excellent job of very narrow band temperature control with NO screwy fan speed switching. In addition, it is using the conventional tstat furnace control wire that the trailer manufacturer put in, quite well. It does not seem to need telephone wire. As long as there are 3 conductors available, it seems to do the job.

I absolutely agree that the tstat placement by the trailer manufacturers is terrible, and has a great influence over temperature control. But, in my case, the new tstat went in the exact same place as the old one--way up the hall behind the bathroom door when open. But the temperature control is night and day better--I have to attribute that to the many button tstat and control board. It is quite possible to have two problems--placement and the few button tstat. My experience with the few button unit was very poor temperature control and screwy fan switching--both solved by the many button and its control board. There are those on line who have absolutely no problem with the few button--not my experience with the OEM or a complete re-installation of tstat and control bd. To be clear in my case the equipment was a MUCH bigger problem than the placement of the tstat (which is still not in a good location).

lenr wrote:
Off the road now with more time to write. Some folks seem to have no problems with the 3 button Dometic thermostat--others. me included, have nothing but trouble. Since the thermo sends communication signals, it takes the AC a moment to change fan speeds; so it sounds like it is stopping as it changes speeds. Unfortunately, this appears to be the design of the unit. Pretty poor design IMHO. The other problem which I experienced was that the thermo doesn't seem very accurate. You can tell what temp it thinks it is by turning everything off and then pushing the + or - button.

There were some early faulty thermo/control board problems which I also experienced, that when the unit was switching off from low would cause it to pause for 2 seconds, then switch to high fan, then turn off. the solution for us was to pay to replace the thermo and control board at our own expense. While that solved the screwy turn off problem, it still would not run in low fan continuously. In addition, when the thermo was trying to start the furnace, the control board in the AC would make lots of clicking noises that were so load they would wake up.

For us our problems were solved (we hope) by the second Dometic AC failure in 10 months. When our OEM unit went out a few months out of warranty, Dometic gave us replacement parts but we had to pay the labor. 10 months later the replacement went out. It seems that Dometic has a high failure rate with Chinese manufactured AC units. Being in a time crunch 2 days into a 2 week trip, we opted for a Dometic scratch and dent unit made in Elkhart and a 10 button control. I wanted to switch to Coleman or Atwood but there just wasn't time or parts availability. The 10 button thermostat seems to work way better than the 3 button. It still uses communication signals, but it doesn't have the obnoxious pauses between fan speeds. The speeds just switch. Also, the thermo seems much more accurate in relation to the actual temp. in the trailer. I believe that the 10 button can be installed on any Dometic by a competent shop. But the better solution would be Coleman with a household thermostat.

They are called 12 button tstats. They cannot be installed where this postings SINGLE Zone tstat is used. This post, the tstat is called a Single Zone and uses its own upper control board and uses only 3 tstat wires. The 12 button requires its own control board AND a phone type cable for communication. So, to install a 12 button would require a new tstat and a new upper board AND run a telephone type cable from the upper unit to that wall area for the tsat. The PLACEMENT of the wall tstat is critical. People blame the Single Zone when the actual problem is the OEM installing the wall Stat in the wrong place. There are millions of these single zones out there and very few problem with the tstat itself. It is usually the install by the OEM that causes the problems. Doug

Ok, after reading all the replies I think I have it figured out. The pause must have been as short as 1-2 seconds, remembering events of a week ago gets harder with age ;) I had the fan on auto both times at start up so it must have been the fan speed adjusting. I'll just keep it on low fan when running AC. The temp really was 67 that morning, I have two thermometers (one digital) and they both read 67 so I guess the thermostat is not very accurate. Thanks for all the replies, I guess I'll just wait until the DW complains and replace it then.

Off the road now with more time to write. Some folks seem to have no problems with the 3 button Dometic thermostat--others. me included, have nothing but trouble. Since the thermo sends communication signals, it takes the AC a moment to change fan speeds; so it sounds like it is stopping as it changes speeds. Unfortunately, this appears to be the design of the unit. Pretty poor design IMHO. The other problem which I experienced was that the thermo doesn't seem very accurate. You can tell what temp it thinks it is by turning everything off and then pushing the + or - button.

There were some early faulty thermo/control board problems which I also experienced, that when the unit was switching off from low would cause it to pause for 2 seconds, then switch to high fan, then turn off. the solution for us was to pay to replace the thermo and control board at our own expense. While that solved the screwy turn off problem, it still would not run in low fan continuously. In addition, when the thermo was trying to start the furnace, the control board in the AC would make lots of clicking noises that were so load they would wake up.

For us our problems were solved (we hope) by the second Dometic AC failure in 10 months. When our OEM unit went out a few months out of warranty, Dometic gave us replacement parts but we had to pay the labor. 10 months later the replacement went out. It seems that Dometic has a high failure rate with Chinese manufactured AC units. Being in a time crunch 2 days into a 2 week trip, we opted for a Dometic scratch and dent unit made in Elkhart and a 10 button control. I wanted to switch to Coleman or Atwood but there just wasn't time or parts availability. The 10 button thermostat seems to work way better than the 3 button. It still uses communication signals, but it doesn't have the obnoxious pauses between fan speeds. The speeds just switch. Also, the thermo seems much more accurate in relation to the actual temp. in the trailer. I believe that the 10 button can be installed on any Dometic by a competent shop. But the better solution would be Coleman with a household thermostat.

One problem and this affects ELECTRONIC thermostates more than any other, is placement.

If the T-Stat is not properly placed then it can pick up either heat or cool from the A/C discharge.. Sometimes simply re-adjusting the outlets will fix.. Back when this house was new, in the winter I had to put a fan on the A/C temp sensor blowing from some distance away or it would do strange things..

So, if it continues to do that, Feel for air flow around it and if needed.. Give it a fan club.

My AC unit has a 3-speed fan. On initial start-up when room temp is high, it will start and run at high fan speed, then pause (shutoff) and shift to a lower fan speed. This is all automatic. I do have the same thermostat as you in my '14 5er. The pause does not last more then a second so maybe that's not your problem.

Note that thermostat placement has a lot to do with the temp it 'reads'. One of mine is in a hallway and when the sun shifts around and comes in a nearby window it heats up that area more then the rest of the camper causing the AC to run more then I want it to.

You state that the real temp was 67 - but does that reading come from a different thermometer that could be affected by something ? Has it been closer to the set temp on the thermostat in the past ?

I have a couple thermometers scattered around my rig but none of them ever match exactly what I set on my thermostat.

moved from technology

Characteristic of that style of Dometic especially early ones. Replacing thermostat and control board might help. I had a lot of trouble with orig and a real enemy. 10 button style works much better. Both send comm signals done the wire so replacement with household style will not work.

Mine is just as goofy. I turn it on and cross my fingers. New ac unit too

Is it possible where you are staying has bad electricity... low voltage or power spikes ?