The A/C light flashing on 88-94 is letting you know the control head detected too-frequent compressor cycling, indicating a low charge. Due to this it has disabled your A/C. You can clear the error in the control head by momentarily disconnecting your battery and then see if the A/C works after you reconnect. If the charge is just a little low, it will run a short while and after it cycles too many times it will set the error again and disable A/C, with the flashing A/C letters you're familiar with already.
There's also a TSB out where this feature of the control head can erroneously set the code, and fixing it requires removing the wire from the control head that allows it to set the error. Someone just recently did a write-up here with the info in it. ->
http://www.gmt400.com/forum/showthread.php?25539-88-94-A-C-Repair-(How-to)
Richard