a/c clutch not engaging

I replaced the A/C clutch on our 99 Mitusbishi Montero Sport. After installing, when I push the a/c button, I do not hear the clutch engage like I used to prior to replacement. I think the possible problems are below. Can you comment on what you think?

1. I might have put in too many shims and the gap is too big. The original clutch had one shim and I put in 3.
2. Wiring is not hooked up right. However, the 2 harness plugs seem to rule this out.
3. The system is discharged. This is probably not putting any compression pressure on the unit and it is actually engaging but you cannot hear it.

thx, Bill