2000 F-250 A/c

A/C blows nice and cold for about five minutes, then starts to cycle cold for three mins or so then barely cool for one min or so then cold for three, etc.

I checked the freon and it is at 32 psi and I believe normal is 25-44 psi so I'm right down the middle there. I am at my limit of knowledge now and looking for some idea's, and info so if I have to take it in I will know if the guy is trying to BS me when he tells me what is wrong with it.

Thanks in advance for all your help.