2003 GMC Sierra Air Conditioning

I anyone can help that would be great. I try to run my a/c and it works for a little but then turn it self it is a automatic climite contril. I jump up the low pussure switch and nothing. So check the relay under the hood and its good. But when I jumped out the relay the compresor turns on. So I rplaced the relay thinking it was weak and still no cool air all the time. You can e-mail me at mrtrout@verizon.net

Its hot and I need some releaf.

thankyou
Jerry