85 Suburban A/C question

[SBTork]

A few nights ago I threw a charge of R12 in my 85 Burb after work, I work at a GM dealer that still has an R12 machine The suburban has rear air too and now it works awesome, but the front a/c does not blow cold. I also put dye in it and plan on checking for leaks, but I am not convinced that's the issue. The compressor kicks on and off just fine and has no obvious problems. Has anyone had this problem and found a solution, or know of one? I am thinking maybe I just don't have enough refrigerant in the system, possibly a switch or something but I am not well schooled on a/c.

Any ideas or suggestions?