I am having a problem with the new AC since I installed it about a month ago. It is a Dometic 15K AC with a new LCD Thermostat kit. This is a ducted system. When running in Auto, the fan will start and run for about a minute but the compressor does not start. This will occur 2 or 3 times and then the compressor will start. This problem normally occurs only at night. I live in Kissimmee FL, so the temperature is in the low to mid 70’s at night. If I lower the thermostat 1 degree after the fans comes on, the compressor will start immediately. I have tried another new thermostat and control box and still get the same result.I changed the freeze sensor. Added additional foam insulation between the air inlet and outlet. Monitored the voltages at night and did not find any changes.Please let me know if you had any suggestions.

We had one like that in our last rig. Think what its doing is checking the air for temp. It the temp is not to high it does not start the compressor and it may start and check air temp several times and not turn on the compressor. We now have a built in AC in one of the bedrooms in our home that does the same. I decided if you check the time between fan runs it may be on a timer so its just checking air temp. Its trying to save the power from running the fan full time. Not sure there is a cure and it is the smart way to go, I guess. But I just gave up and run the fan full time. The starting and stoping of the fan bothers me more than running it full time. I also question the amount of extra power it takes to start the motor several times over just letting it run..

Mine pretty much does that as well. It will even turn the fan on low when the temp is close to set point. and then switch to high when needed. Hard to get use to. But it works well

Any vents pointing in the direction of the thermostat?

Moved from Forum Technical Support

1. Your first complaint. Are you saying the fan comes ON and then goes OFF after a minute? Then it comes back ON and then turns OFF after a minute? 2. The normal delay of a RV roof top system is up to 2 minutes 45 seconds time delay before the compressor comes on in Auto or in Hi or Lo fan. If you leave it for 5 minutes does the compressor ever come on? Doug

Dometic AC in auto mode | Good Sam Community

DR650
Explorer
Jul 17, 2013
I have a window unit air conditioner that will cycle the fan every 10 minutes to sample the air temperature. It may take 3 to 4 cycles of the fan only before the compressor kicks in and begins cooling. The purpose of this is to maintain a more consistant temperature in the room. I'm not sure if the newer RV air conditioners operate this way or not.
jfschmitter1
Explorer
Jul 17, 2013
There are no dip switches on this control.
Joe
dougrainer
Nomad
Jul 17, 2013
I have not had to mess with the DIP switches much on the new tstat system. ARE YOU POSITIVE that the control Board DIP switches are set correctly? Doug
jfschmitter1
Explorer
Jul 17, 2013
This is not a heat pump.
I do have the analog tsat and control from the old Dometic unit. I was considering installing it to find out if it solves the problem. Is this compatible with the new unit?

Thanks
jfschmitter1
Explorer
Jul 16, 2013
Yes, I did replace the freeze sensor.
wa8yxm
Explorer III
Jul 16, 2013
I do have a suggestion....... And a possible cause.

The fan starts, a precision timer is sometimes included in BETTER air conditoners before the compressor kicks in in order to prevent "hot starts" where, for example, a power "flicker" shuts it down and it tries to re-start before the pressure has bled off.

Due to the air moving about the t-stat now senses "Cool enough" and shuts down.

Finally it's hot enough even with the fan running and it continues to operate.

The suggestion:

Many times I hear complaints about A/C Noise.. The solution to that is to run the fan on HIGH, not automatic.
Your brain will very quickly "Filter" the sound of the fan and the blower "noise" which approximates white noise will also mask the kids and dogs on the next site (won't completly block 'em but will mask 'em) so you win, win, win with the blower on high.
dougrainer
Nomad
Jul 16, 2013
When you replaced the control after the first failed, did it come with a NEW freeze sensor? That is the only thing that I can think of that "may" cause your problem, but not likely. Is this a Heat Pump? Doug
jfschmitter1
Explorer
Jul 16, 2013
The voltages are 119.5 and 13.6

Joe
dougrainer
Nomad
Jul 15, 2013
jfschmitter1 wrote:
I have checked the 12v and 120v day and night and have not found any problems.
If I lower the thermostat 1 degree while the fan is running, the compressor will start immediately.
Is there a temperature sensor that may be causing this?

Thanks
Joe

NO, the wall tstat is the temp sensor. WHAT is the voltage both 12 volt and 120? Doug
jfschmitter1
Explorer
Jul 15, 2013
I have checked the 12v and 120v day and night and have not found any problems.
If I lower the thermostat 1 degree while the fan is running, the compressor will start immediately.
Is there a temperature sensor that may be causing this?

Thanks
Joe

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