Not sure if your problem is exactly the same as mine, but I've been frustrated by my A/C kicking off as well. I have a '94 850 Turbo. I'm one of the many people who spent big $$$ to replace the evaporator 2 yrs ago, but noticed on very hot days when the car was sweltering, the A/C would always kick off after 2- 4 minutes of driving. Quite annoying when you are on the open highway. If I turned the car off and restarted it, the A/C would resume again. Not a good solution to keep stopping and restarting the car.

After much experimentation with the control settings, high, low etc. I found a good work-a-round to keep the A/C consistently on without cutting off.

First, I do not use the AUTO setting on the FAN control nor do I use the FULL BLAST under 60 degree setting on the temp control. Here's what I do.

I set the temp control to 75-78 degrees.
I use the manual fan setting on low.
I keep the windows down until the interior of the car begins to cool off.
Once it cools down, I close the windows and GRADUALLY move the fan setting higher and the temp setting lower, but NEVER down to the max temp control.
I also run it in REC mode.

Works like charm and now it never cuts off. I'm not saying the car is freezing, but it gets very comfortable and the darn thing works consistently. This does take patience as you will be a little hot hot for the first mile or so. But it works for me and it's taken me 2 yrs. to arrive at this method. After spending $850 on new evaporator, I'm not spending another cent on A/C.

Try it out and let me know if it works.