a/c works after about 10 minutes

Have a 97 blazer and the a/c will not work for about 10 minutes after you first crank it, then once it comes on it will continue working for the rest of the day. It only happens the first time you drive it. Possibly a faulty relay?? Please help..
I jumped out the low pressure switch and it does nothing, not low on freon.

Thanks,
Matt

Low perssure, get a refill kit and top up your refrigerant.