Congrats on your camper and welcome to Sunline Owners Forum.
On the AC unit, I do not know the model number of the one in your 83 camper, but I do know some on ones from the 90's and forward.
I'm not exactly sure what you are saying,
The a/c runs and then shuts off and then runs again a few minutes later. Maybe it's down to temp, but shouldn't the fan still run if the switch is on to fan?
Assuming you have an "older" AC unit and this is a Dometic AC unit, meaning at least year 2010 ish and older, (the brand news ones are different) The AC unit runs to satisfy the T Stat. The fan and compressor run together for a time period that satisfies the T stat. Once the T stat is satisfied, then both the compressor and the fan shut off. There may be a delay on the fan to run but once the T stat is happy, it shuts off.
As time passes and the T stat warms up, then both fan and compressor run again. This is how they worked.
If you want the fan to run, some had a fan switch that allowed just the fan to run, but if the fan was in "auto" mode, then the fan would cycle with the compressor.
Now knowing this, what is your unit doing? If you say it runs and shuts off, how long is it running for? 5 to 10 minutes or trying to cycle every 30 seconds which is a problem. If the T stat is satisfied, it could be doing what it is supposed too. Unless it has issues. The new digital T stats are good to control within +/- 1 deg F. The older analog ones, they could be up to +/- 3 to 4 deg F.
If you crank down the temp a large amount, say 5 to 10 degrees from ambient, it should run close to non stop trying to get to the setpoint and once at setpoint, (or what it thinks is setpoint) fan and compressor shut off. Does this work?
The brand new units are different. On those, the fan runs non stop period. And just the compressor cycles on and off. There are many of us who actually do not like this new feature. We are camping and the lack of noise is pleasing. I bought new upper unit last year and on purpose used my old control box so the system would shut down. But again, that is personnel preference.
If we need to dig in deeper on this, we are going to need a model number of the AC unit so we can look up exactly what you have. And the brand in case someone changed out the original Dometic unit. If it is a Coleman Mach, it may have been changed. I do not know for sure, but I think Sunline only used the Dometic.
Hope this helps