Serpentine belt swap woes.

[CN84C10]

Hello all,

About a month ago I swapped over to the serpentine belt setup on my 84 C10.
I used a setup from a 93 pickup. I got the A/C working and all was well until I noticed that on the compressor the belt was trying to walk back on the pulley. I also noticed that the tensioner would bounce back and fourth quite a bit. So I replaced the belt with one approx 3 inches shorter. This seemed to fix the problem with the tensioner bouncing, but I noticed this morning that the belt is still trying to walk back on the compressor. It will move one groove back then it will begin cutting the belt on the last groove. All of the accesories are in a fixed position, what could cause this to happen? I thought maybe I put the P/S pulley on too far, but the belt rides fine on it and all the other pulleys. Its just the A/C comprerssor that is causing this problem. Any suggestions?

Thanks in advance,

Chris