It could be several things.
Could be the lower preasure switch on the drier. To see, you can just jumper it. If this works you will want to check the systems charge.
If that's not it, it could be the compressor relay. The compressor relay is on the passenger side fenderwell area. Should have the following colors on it, light blue wire from the A/C cycling switch which should measure +12 still, a pink/black wire which should have +12 on it with key on , a yellow wire also which should be grounded by the ECM when A/C is called for.
It also could be the switch on the AC slider. I've had this happen to me twice now.
If you don't already have a wiring diagram, now would be the time to get one. They come in handy in times like these.
HTH.