Short story:
I bought my current '87 300D in LA, drove it home to MI. It was fairly cool weather so I selected the economy setting, no A/C. Periodically the A/C compressor would come on, and I'd get cold air out of the vents. I'd push the off button and then back to economy, the compressor would stay off. Eventually the compressor would come on again and I'd repeat the process.
At one point I decided to turn off the climate control, it was night and I had the windows open. To my surprise, the A/C would still come on occasionally, fan and all, I'd have to cycle through the on and then off again to kill the A/C temporarily.

When I returned home, I installed a NEW CCU, all was well. I also unplugged the aux. pump to avoid possibly damaging the new CCU until I could test it (it was seized I found out later).

Anyway, your symptom is slightly different than mine was, but similar in that it turns on and off or seems posessed. Probably a bad CCU, unfortunately. Finding what made it bad is another concern of course, but it sounds like you have found a bad aux. pump which might have damaged your CCU.

__________________

Gone to the dark side

- Jeff