I just charged my ac to 40psi on the low side and now it wont work and the gauge says its at 70psi which is out of range for the compresser to work. It worked for a total of about 40mins after recharge. Now no cold air what should I check first. The truck is a 95 1500 4x4 with a 305 5 speed if that makes a diff. 134a freon

What exactly did you do to the A/C? Was it working before? Check the lw pressure switch as GM's crummy design wreaks havoc on them. Also what is your high side pressure? Some A/C systems have a high pressure switch to disable the compressor until it is charged to a certain point.

just put in more freon and no didnt work until I did that.

dont have a way to check high side