Air Conditioning problem
1972 Volvo Wagon 4 cyl Two Wheel Drive Automatic 98,000 miles

I am asking this question for my son who lives in another city - recently on a visit during this hot summer, he & his family experienced their A/C cutting out, especially during acceleration, passing and climbing.

I didn't have a chance to check for slipping belts- is that a possibility or is the compressor giving out ?
Thanks for you time & expertise !
Have always loved the show !