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jfschmitter1's avatar
jfschmitter1
Explorer
Jul 13, 2013

Dometic AC in auto mode

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.
  • dougrainer's avatar
    dougrainer
    Nomad
    Jul 14, 2013
    jfschmitter1 wrote:
    1. Yes it runs for one minute then shuts off. Then there is a delay of about 5 minutes and it repeats. After 3 or 4 times the compressor will come on.
    2. Under normal running condition the compressor starts 10 to 15 seconds after the fan.
    3. The problem with the compressor not starting normally only occurs at night, between approximately 10 pm and 7 am.

    There are no vents directed toward the thermostat.


    You need to check the LINE voltage since this problem happens only at night. You also need to check the 12 volt supply AT the AC control box when this is happening. 12 volts is what operates all the relays and controls in the AC control board. I suspect you have a 12 volt supply problem. I have worked on(and correctly fixed) thousands of RV AC systems over the years and have NEVER experienced your type problem. Since you have replaced the Tstat and control box, your problem is external to the AC system. Doug
  • jfschmitter1's avatar
    jfschmitter1
    Explorer
    Jul 13, 2013
    1. Yes it runs for one minute then shuts off. Then there is a delay of about 5 minutes and it repeats. After 3 or 4 times the compressor will come on.
    2. Under normal running condition the compressor starts 10 to 15 seconds after the fan.
    3. The problem with the compressor not starting normally only occurs at night, between approximately 10 pm and 7 am.

    There are no vents directed toward the thermostat.
  • dougrainer's avatar
    dougrainer
    Nomad
    Jul 13, 2013
    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
  • Terryallan's avatar
    Terryallan
    Explorer II
    Jul 13, 2013
    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
  • snowdance's avatar
    snowdance
    Explorer
    Jul 13, 2013
    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..

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