Auto Air Conditioning & Heater Repair: Pontiac montana on/off air conditioning, pontiac montana, pressure gauge

Question
on my 2001 Pontiac Montana the ac will very seldom turn on when the ac button is pushed then when it does turn on the system will turn off at will usually 1-2 minutes latter.  Sometimes turning off when I adjust the fan blower speed but not always.  Then sometimes while driving the ac will turn on by itself sometimes running for several minutes sometimes for only seconds.  When it does run the ac is very cold and makes no unusual noises.  The ac button has a light to show when operating and it is accurate for showing when the compressor is on or off.  The problem seems to be getting worse as in the ac will not engage as often as it used to when the ac button is pushed.  I don't know if the engage switch is malfunctioning or the pressure switch is bad. or ????????  help please.  P.S. I did get a chance to hook up a pressure gauge to the ac when I caught it running and the pressure showed to be borderline between charged and over charged but was not showing overcharged however the system was only running for 20 sec.   Thank you

Answer
Jeremy,
All I can say is WOW. All kinds of headaches.
From the sound of it, you were right in your assumption. I would say that something in your control head is definately causing the problem. I won't necessarily say that it is the on/off switch with the light on it, but that is certainly a possibility. Or on the lighter side, it also acts as though there is a loose connection somewhere on the output plugs, being that it isn't just the compressor acting up, but the blower motor affects it also. And the way it turns itself on and off would also give more evidence towards a loose connection.
I would first check the connections coming from the back of the control head. If they are all tight and secure, then as bad as I hate to say it I would recommend taking it in to a reputable shop or even, dare I say it, dealer *shiver* for them to troubleshoot further. If it comes down to it being a fault in your control head, then it may be cheaper to find one in a used parts yard. (junkyard).
I wish I could be of more help, but without the vehicle and schematics in front of me, this is all I am able to give you.
Sorry for so little, but thanks for your question.