It sounds like the classic "cold solder joints" problem.
there was a really good write up on the web. Maybe someone can point you to it.

 

You have a bad relay somewhere.
Your AC if fine; the button is fine; its just a bad relay. Find it or hotwire a switch into your dash to make it work.

 

Here is the link for the logicon cold solder joints problem, as well as fixes for numerous other problems!

http://teamfc3s.org/faq/index.shtml

None of the buttons on my logicon would work (the LED wouldn't light up). I pulled the thing out and found several cold solder points. Re-soldered and they all light up now (but the A/C still doesn't work - no freon).

Also, check the A/C pressure sensor connections. If there isn't any freon, I believe the compressor won't turn on.

Good luck.

 

It also might be low coolant. The A/C system is designed with a sensor that won't let the a/c come on when there isn't enough coolant in the system (so you won't burn up your compressor).

An easy way to check your compressor is to unplug the black wire from it and touch it to the neg battery terminal. The clutch should engage.

If you suspect your logicon, before you do any solder work, make sure it's all plugged in. (I got bit by this one). Pop off the top part of the dash, remove the little center plate and remove the screw holding the dash piece down. Kinda move it outta the way and look down there, driver's side center area, and make sure the plug is seated firmly.

If all that checks out, I'd replace the relay at the front of the vehicle. There are two film-canister lookin' things there. One or both control the a/c.

Good luck!

 

what is a cold solder point? I'm sitting here looking at my logicon, perplexed. Please help before I get out the BFH.