I have been chasing this annoying problem for several years now with no luck. Most of the time the compressor will engage and the a/c will work on the first start of the day; but occasionally it locks itself out where the compressor will not engage on initial startup. Restarting the car usually fixes it, but sometimes it takes several attempts. What is strange is that when the compressor does engage on the first start of the day, it always seems to disengage about ten minutes into the drive. When I restart the car it usually goes back to engaging, but sometimes it takes a few attempts. I have always been able to get it to work, but on rare occasions it has taken quite a few restarts.
The codes I'm repeatedly getting on pin 8 are DTC 6 (a/c clutch jammed or v-belt broken) and DTC 7 (poly-v-belt slips). I have replaced the compressor (including speed switch), receiver/dryer, expansion valve, interior temp sensor, poly-v-belt and just installed a new factory tensioner (3rd version). Even tried some belt dressing with no improvement.
I thought the new tensioner would finally solve the problem but it didn't. The system is properly charged and the pressures are within spec. When the compressor operates it cools well -- It either works well or it doesn't work at all. I always run with the temperature selector in the max cool position here in Arizona, so I think this would bypass any issues with the tempersature control head.
So, what's left to replace on this? Any thoughts? I'm thinking of swapping base modules next to see if that's the problem. Thanks.