a/c problem

A friend bought a 97 Chevy truck a few months ago and the a/c never has worked, we had no prior history. They brought it to me and I found there was no refrigerant in the system so I vacuumed it and it didn't seam to leak so I put two pounds of 134 in it per the label under the hood. I started it, the compressor kicked on and the system stabilized at 100 psi high and 80 psi low. The compressor made no unusual noises so I assume it was pumping so my guess is maybe the orifice tube is missing. Can anyone tell me where it is suppose to be in this truck or am I jumping to the wrong conclusion? I'm open to other possibilities. Thanks for any help.