88 190E AC problem

[cfxxc]

Hi
The AC on my 190E works great most of the time, I have checked all the usual things, Presures, compressor control, coolent & evap temp sensors, belt tension, comp clutch, all appear to be with in limits.
What is happening is that the AC comes in some times for half hour or maybe longer and then just quits then some time later it will come on again or if I stop the car and turn it off some times it will come on again some time not.
The problem seems to be worst when the ambient temps are higher above 75F.
It will work all the time when I ground pin 10 on the comp control and it will produce vent temps of 40F or less if I let it.
When I first bought the car the AC would not run at all, I thought it was th PBC so I opened it up to see if any thing was a miss but found nothing so I put it back in plugged it in and it works some times.
Do any of you folks have any suggestions.
Thanks
Chuck