I have a '96 Devil and the AC control will not switch form "ECON" to "AUTO", so the AC pump never comes on. When I push the "AUTO/ECON" button, the LED shows it switching to AUTO, but as soon as I let go of the button it goes back to ECON. One day it was working fine, and then suddenly it didn't, so I am thinking it is an electrical issue. I checked the refirgerant level and it is good. Fuses in the fuse box are good. I replaced the AC relay in the fuse box just to be sure. So all the easy fixes have been tried.

** Update on the problem**
I disconnected the battery for a few minutes, to reset the computer, and the A/C worked normally for about an hour, then the problem returned (it was a very hot day, for Denver Colorado). I reset the computer again, and now it has worked for two days, which amounts to about 3 hours of my wife cruising around town.

What could be causing this????

 

I had that problem about three weeks ago, i had my ac converted over to the 134a. but the ac never came on, even on defrost it never came on. then i found out that computer needs to be cleared of fault codes. so i got info on how to clear. then the ac come right on. hope it helps you. Cadillacstyle

 

If you have no codes, you are low on freon!!

 

Could also be your Ambient sensor or the in car sensor, which is for temp. set.