AC Function

[BigJohnD]

Figured I'd try posting this on the CC side since I hadn't see much response on the tech side.


On the typical day, we operate our AC with the temp set, and the fan in auto where it will cycle on and off during the day. At night time, we set the fan to low or high, and let the AC compressor cycle on and off all night. We like the noise.

One strange thing that's going on, is when we get up in the morning and turn the fan back to auto, it will not shut off, even if the compressor is not running. The fan will just stay running. However, you can turn the whole thing off, then back on in auto and it will cycle on and off like it's supposed to.

Any ideas? This is one of the late model Dometic 15K units with the digital thermostat.

[greysailor]

Howdy john,
No answers here, but it sounds like the programming likes to be rebooted before it recognizes that functionality. On past motorhomes, I never had much luck with the A/Cs working properly with fan in auto anyway....they seemed to freeze up on me because the older Dometics only ran fan on low speed when in auto. I'm about to pull my RV over to the dealer for some service work, but before I leave, I might try to duplicate your setup and see what happens.

[BigJohnD]

Thanks greysailor. I agree with the auto / low speed deal. In the past I've had a lot of units freeze up on low speed. So far, we've been fine, but it hasn't got hot yet requiring the unit to run for long periods. On our last motorhome, same t-stat, it would switch back and forth from high to low speed when in auto mode, but it never could make up it's mind what it wanted. Might run for a minute in low, then to high, then back.

It will only do what I mentioned when the unit has been running for a while. If it entails changing the control box out, I might not even mess with it, as it still does work, just not how it's supposed to. We can't bring it to the dealer, or lets just say its a major inconvenience as this is our home and we can't move out for a couple of days for them to research, and I usually just fix everything myself when possible. Warranty probably wouldn't send ME a control box anyway.

[awwall]

John, just curios..how long do you wait before you "reset"? Wonder if it takes a couple of minutes before it realizes that the thermostat has been changed?

[BigJohnD]

When it has worked correctly (assuming we've only run it for a little bit for test purposes), you swap to auto and less than 5 seconds it turns the fan off. When it wouldn't shut off (after running all night), we had switched the fan to auto and waited 5 minutes before turning the whole unit off.

[awwall]

Just a wild guess. Sure sounds like a thermostat problem. Have you contacted Dometic? They seem to have good customer service. Maybe they will send you a new one out. Only a 3 wire hookup.

[Elkrun]

John,

I think I have had the same problem in the past.....I was just wondering if there is a sensor in the Dometic that waits until the coil/compressor has reached a particular temperature before it finally turns off? Don't know just a guess. I'd like to know the answer to this as well, in my case I thought it was just the way I had T-stat programmed.

[BigJohnD]

Only reason I haven't contacted Dometic, is they usually give me the "bring it to your nearest authorized dometic service center" deal. They've never been much help after I tell them I am the nearest service guy and I do my own work. Just won't volunteer much help, I guess due to liability or something. Never mind I've changed / installed several AC's, control boxes and t-stats.

This wouldn't be the first 3 wire LCD thermostat I've had trouble with. Replaced the one in the Forester as well. I really hope that is all it is, as that's a quick easy fix. I may give Dometic a call, but don't expect much help.

[ret2006]

I had a bad Dometic Comfort Control II thermostat in my new CC 34 RLSA. It would short cycle the air conditioners. My dealer sent me another one and that corrected my problem. The new Dometic thermostats don't seem to be of very good quality. Wish a good Honeywell would work but I don't think they will.

[BigJohnD]

I agree. I had a Comfort Control t-stat in our Mobile Scout fifth wheel, and it was a lot nicer. These new ones have not impressed me at all. One of the biggest things I hate is when it decides to swap fan speeds, the blower completely shuts off for a second, then back on in the next speed, where as the older ones made a smooth transition between speeds without shutting down.

[bob34787]

every one that I had did the same thing, finally I just shut the system off than turned it back on, worked fine. Had to do this every morning

[BigJohnD]

bob, just to clerify, you're referring to the fan not turning off when switched from low or high speed to auto as mentioned in my first post?