Originally Posted by AVid
Ran into a slight problem this weekend on my son-in-laws trailer. The AC works fine if you set the temp and run the fan on AUTO. The compressor starts and stops just fine. But....if you set the temp, run the fan on LO or HIGH, the compressor will run until the set temp is reached then shut off, leaving the fan run. However, the compressor will not start again.
I know what I know, and I also know what I don't know....and I don't know AC systems. My best guess is the thermostat is faulty. Anyone have any insight that may help us out?
I assume you have the Dometic Digital Thermostat as you didn't state what unit you have.
I had a very similar (But not identical) issue not long ago I will share with you in hopes it helps you.
In the Auto Fan Mode my compressor and fan would run like they should until the compressor cycled off one time, then the fan would kick up to high speed and the compressor would never run again no matter what. You could turn the whole system off with the thermostat On/Off Mode button, turn it back on and it would cool fine until the compressor cycled off again.
If you ran the air conditioning with the fan on High or Low speed, the compressor would cycle on and off as needed and the fan would continue to run as it should on the chosen speed continuously with no issues ever arising.
I first suspected the thermostat, but after researching and finding the thermostat is more of a control head and sensor that is merely sending signals to the control box I started second guessing my thoughts. Then, when it also appeared that you can either purchase the thermostat or a Thermostat/Control box kit, but not just the Control Box, I opted to purchase the kit knowing if I bought the thermostat alone and that did not fix the problem I would end up with an extra thermostat when I bought the kit. I figured one day I may need the Control Box even if it wasn't my issue now.
Ordered the kit ( Dometic 3313189.000 Single Zone LCD Thermostat and Control Kit Polar White Trailer Camper RV
) for $75, the thermostat is $30-35 by itself.
I did install just the thermostat by itself first because I am one of those guys who has to know what fixed the issue, not just fix it and be happy. I want to understand it. It turns out I did have to replace the Control Box portion too. So now I have a back up thermostat anyway, but at least now I know more about how the system works and how to go about diagnosing any future issues.
One note, when you do replace the thermostat, control box or whatever, there is a "System Initialization" procedure that should be performed. It is in the instructions but can be easily overlooked. Ask me how I know.
I hope this helps you, if not maybe it will help someone else in the future.