New Dometic 3 button thermostat shuts down AC system at will

[RobertL0]

We have a 2015 Coachman with the Dometic 3 button thermostat, running their 15K BTU unit.
When in AC mode, (fan speed set to low or high), the RV will get to it's set point, then the compressor AND the fan will shut down at the same time. I'm NOT talking about having the fan speed on auto.

There are no temperature sensors in the RV , other than the one on the thermostat.

For me to restart the cooling, I need to shut off the AC via the thermostat, and then turn it back on. The problem will the repeat itself.

I would rather do the work here, then leaving the RV at a service center for a few days if I can, especially in the mid of summer camping.

Think replacing the thermostat will do the trick? Are there better thermostats out there than the Dometic?

Thanks in advance

[dougrainer]

Vulcan Rider wrote:

MM49 wrote:
It could be condenser freezing also. I notices mine is dumping a lot of water during this cycle.
MM49

It is also possible that it has a "high water" float in the collection tray that will shut it off if the drain hose is plugged or otherwise not draining fast enough.

They do not have such a float on RV AC units. Doug

[Vulcan_Rider]

MM49 wrote:
It could be condenser freezing also. I notices mine is dumping a lot of water during this cycle.
MM49

It is also possible that it has a "high water" float in the collection tray that will shut it off if the drain hose is plugged or otherwise not draining fast enough.

[MM49]

RobertL0 wrote:
Thanks, but I am able restart the unit immediately by shutting it off, then on, via the thermostat..I think high head pressure would prevent me from starting the compressor immediately

MM49 wrote:

RobertL0 wrote:


For me to restart the cooling, I need to shut off the AC via the thermostat, and then turn it back on. The problem will the repeat itself.

I would rather do the work here, then leaving the RV at a service center for a few days if I can, especially in the mid of summer camping.

Think replacing the thermostat will do the trick? Are there better thermostats out there than the Dometic?

Thanks in advance

Your problem is real. I have a new Sunny Brook with the same issues. It seems like it is cutting out from high head pressure. It resumes later. This only happens in very hot weather.
MM49

It could be condenser freezing also. I notices mine is dumping a lot of water during this cycle.
MM49

[RobertL0]

Thanks, but I am able restart the unit immediately by shutting it off, then on, via the thermostat..I think high head pressure would prevent me from starting the compressor immediately

MM49 wrote:

RobertL0 wrote:


For me to restart the cooling, I need to shut off the AC via the thermostat, and then turn it back on. The problem will the repeat itself.

I would rather do the work here, then leaving the RV at a service center for a few days if I can, especially in the mid of summer camping.

Think replacing the thermostat will do the trick? Are there better thermostats out there than the Dometic?

Thanks in advance

Your problem is real. I have a new Sunny Brook with the same issues. It seems like it is cutting out from high head pressure. It resumes later. This only happens in very hot weather.
MM49

[MM49]

RobertL0 wrote:
We have a 2015 Coachman with the Dometic 3 button thermostat, running their 15K BTU unit.
When in AC mode, (fan speed set to low or high), the RV will get to it's set point, then the compressor AND the fan will shut down at the same time. I'm NOT talking about having the fan speed on auto.

There are no temperature sensors in the RV , other than the one on the thermostat.

For me to restart the cooling, I need to shut off the AC via the thermostat, and then turn it back on. The problem will the repeat itself.

I would rather do the work here, then leaving the RV at a service center for a few days if I can, especially in the mid of summer camping.

Think replacing the thermostat will do the trick? Are there better thermostats out there than the Dometic?

Thanks in advance

Your problem is real. I have a new Sunny Brook with the same issues. It seems like it is cutting out from high head pressure. It resumes later. This only happens in very hot weather.
MM49

[campn4walleye]

dougrainer wrote:
I am not assuming they are all alike, I listed the Med, because some do have medium. But the systems all function the same in regards to your complaint. I have 36 years as an RV tech and am Master Certified.

Doug- you have change your name to RV Wizard!...I'm a believer.

[RobertL0]

Was this problem ever resolved?

lenr wrote:
Our newly installed tstat and control board now seem to be not starting up on auto fan. Had it set to 62 with the tstat saying it was 77 with no start. Finally took off and ran after several cycles of the push button thru tell heat-off-fan speed-a/c positions. Can't find a tech support number for Domestic--they only talk to dealers. I don't believe this is a dead band issue. If the dead band is this wide, then this tstat is total junk. The manual says it will switch to high fan when 5 degrees from set point--it does not say there is a 5 degree dead band.

[dougrainer]

lenr wrote:
Domestic had a bunch of bad control boards a few years ago. We just had the thermostat and control board replaced on our digital control 15K a/c system and it solved a few screwy problems. Temperature control is still terrible. Stat is very slow to react. You cannot change to any other stat without rewrite of the control because this one uses only 3 wires including furnace control. The switching between low and high fan uses control signals on one wire which causes the pause between fan speeds. Low on our15K doesn't seem to have much cooling capacity and you only get high when there is 4 to 5 degrees from set point. We end up forcing the fan to continuous high and letting the compressor cycle to get compfortable. Seems like a junk design to me--probably saved someone a $1.95. My son just got a Coachman TT with a Coleman a/c and a manual mechanical thermostat. Kind of wish I had the same!

Dometic did not have a batch of bad control boards. What they had was a batch of BAD Single Zone tstats. The Newer Single Zones back then had round yellow stickers on the tstat to let service techs know which were the updated tstats. NO yellow sticker and you had operational problems ,replace the wall tstat. The original bad batch, IF the interior of the RV was over 100 degrees, then the tstat would not come on and function. LO is LO and HI is HI. Having a different wall tstat will NOT change the fan speed. Doug

[dougrainer]

I am not assuming they are all alike, I listed the Med, because some do have medium. But the systems all function the same in regards to your complaint. I have 36 years as an RV tech and am Master Certified.

[lenr]

Our newly installed tstat and control board now seem to be not starting up on auto fan. Had it set to 62 with the tstat saying it was 77 with no start. Finally took off and ran after several cycles of the push button thru tell heat-off-fan speed-a/c positions. Can't find a tech support number for Domestic--they only talk to dealers. I don't believe this is a dead band issue. If the dead band is this wide, then this tstat is total junk. The manual says it will switch to high fan when 5 degrees from set point--it does not say there is a 5 degree dead band.

[lenr]

Domestic had a bunch of bad control boards a few years ago. We just had the thermostat and control board replaced on our digital control 15K a/c system and it solved a few screwy problems. Temperature control is still terrible. Stat is very slow to react. You cannot change to any other stat without rewire of the control because this one uses only 3 wires including furnace control. The switching between low and high fan uses control signals on one wire which causes the pause between fan speeds. Low on our 15K doesn't seem to have much cooling capacity and you only get high when there is 4 to 5 degrees from set point. We end up forcing the fan to continuous high and letting the compressor cycle to get compfortable. Seems like a junk design to me--probably saved someone a $1.95. My son just got a Coachman TT with a Coleman a/c and a manual mechanical thermostat. Kind of wish I had the same!

[dougrainer]

Vulcan Rider wrote:

RobertL0 wrote:

When in AC mode, (fan speed set to low or high), the RV will get to it's set point, then the compressor AND the fan will shut down at the same time.

For me to restart the cooling, I need to shut off the AC via the thermostat, and then turn it back on.

Sounds like normal operation to me. If the fan runs all the time, your humidity control will be VERY poor.

This is how my house and RV work.....and even some window A/C units too......except for the restarting part, that is.

Are you SURE that turning the temp down 5 degrees or so will not cause it to restart ? (Some will not restart within 5 minutes.)
It is possible that your stat just has too wide a range to keep things comfortable.

If set on Lo Med or Hi fan speed and set for cooling that means the FAN will run continuously on RV units. In MY house, if I set the fan to AUTO the whole house fan turns OFF with the compressor. If I set the Fan to ON, then it will run continuously regardless of compressor on or OFF. Doug

[RobertL0]

Thanks

Things have been working well for the last 2 months. This problem just started, maybe a got a surge from a campground that did something to the thermostat or upper board...

TXiceman wrote:
One thing to check is the power source for the thermostat. It should be fed from a separately fused circuit....ie, nothing else on this circuit. The newer thermostats are prone to interference fed through the power source.

Ken

[TXiceman]

One thing to check is the power source for the thermostat. It should be fed from a separately fused circuit....ie, nothing else on this circuit. The newer thermostats are prone to interference fed through the power source.

Ken