Kaiser,
The system could be under high pressure causing the compressor to cut on and off. Check the following:
1) aircon aux fan- if this is slow or busted then system is overheating.
2) lack of freon or too much freon- watch the glass window atop the aircon drier, should show bubbles when you switch on, then should disappear, then reappear when you switch off. If you see a constant stream of bubbles then you lack freon but if no bubbles at all, then too much freon.
3) Change the drier if they find a leak or clean the system but don't change the expansion valve, unless busted, since these can last the life of a car.
Tell us when you finally find the problem!:wink: