Thermostat reading -05 degrees inside temp

[CJBrent]

I am getting inside temp readings of -05 on my thermostat. Heat pump and furnace work on occasion and AC seems to work fine and cools well. When I attempt to start the furnace or heat pump, they fail to start and the inside temp continues to read -05. The thermostat has been replaced and the techs at the service center claim to have ran all 3 systems for 3 days with no failures. Has this happened to anyone else? Any suggestions?

[MrUKToad]

We collected our Airstream from storage on Friday and found that the thermostat control wasn't working correctly. I could reduce the heat setting but not increase it. After a bit of thought I decided that it may need a reset (too much time on the PC and you know all about resets!). The instruction manual showed showed how to do it and 30 seconds later the problem was solved. Try a reset, it won't do any harm.

[dznf0g]

Contact forum member Lewster.

[Jim Flower]

The heating / cooling system was not working correctly on my 2012 International Sig last year and I eventually found the fault in the telephone line that connects the thermostat and the ac unit. There was a loose connection on the ac end and once it was plugged in properly, all was normal again. To gain access to the plug on the ac, the inside cowling has to be removed by undoing about 6 screws. As you can see, there are a few things that can go wrong. One needs tiny fingers to poke around in the ac and lucky for me, a son was available at the time. Good luck.

[Silver Goose]

Originally Posted by CJBrent

I am getting inside temp readings of -05 on my thermostat. ...

If your CCC (thermostat) ever loses 12v power, results are unpredictable and as MrUKToad suggests, a reset is simple to do, it can't hurt and frequently fixes the problem. If I understand your post, the -05 on the display was your original problem and a shop replaced the CCC for that, never saw the problem, and the new CCC is now behaving the same way, and sometimes the heatpump/furnace operates and sometimes it doesn't. When one or the other does operate, does the CCC display appear normal or is the -05 always visible?

If it comes and goes, it sounds like you have an intermittent problem and that sort of thing is the curse of the service tech and a frustration for the owner. Jim's suggestion to replug the connectors is an excellent next step following the CCC reset. On occasion, a part gets replaced and the problem resolved, but the part was never faulty, it was the physical replugging that was the real fix. Additionally, manufacturers often maintain a database of symptoms that authorized service providers should have access to. If the displayed -05 is significant, Dometic may know what this points to. Hopefully this is happening within the warranty period.

[richinny]

i had the same problem and found the telephone connector mentioned (there are 2) was wet with condensation. one at a time i took 1 out, dried it out with a hair dryer, replaced it and wrapped a sandwich bag around it and secured the ends with twist ties. i've had no problems since.

[CJBrent]

Originally Posted by richinny

i had the same problem and found the telephone connector mentioned (there are 2) was wet with condensation. one at a time i took 1 out, dried it out with a hair dryer, replaced it and wrapped a sandwich bag around it and secured the ends with twist ties. i've had no problems since.

Once I take the interior cover off the unit, are the cables difficult to locate or fairly visible?

[Jammer]

CJ

They've changed the layout a couple of times but in my experience you have to take the thermostat off the wall to get at the connector.

The Dometic CCC thermostat, wiring, and logic boards have as a whole given me no end of trouble. The RJ-11 phone connectors they use are a low-cost connector that performs poorly and are one of several weak points. The next time mine acts up I'm ripping out the whole thing and replacing it with a standard thermostat. The only reason I haven't is the enormous hassle involved in running the wires.

[Silver Goose]

If memory serves me correctly, the other end of the telco type cable from the CCC plugs into the power module board. To access it you need to get on the roof and remove the plastic shroud over the A/C unit (4 screws around the perimeter?). The board is on the curb side of the unit. There may be a sheet metal cover over the board that needs to be removed for access. Disconnect the shore power before poking around in there as there are some exposed 110v connectors in that area. You will see at least 2 of those telco type plugs on that board.

[richinny]

Originally Posted by CJBrent

Once I take the interior cover off the unit, are the cables difficult to locate or fairly visible?

once the inside cover was off they were visible in the center area. as mentioned, it is hard to reach in there but doable. i think i held the wire coming down with two fingers and the connector with a needle nose pliers and pushed it up to reconnect them. ifyou can let them dry out a day or two, you might just have to wrap them.

if you're not familiar with the release clips on phone wires, practice with a phone so you can do it without looking.

i might have had two connectors because i have two ac units.

[richinny]

and yes, powering off the trailer for safety is a good idea.