I had a similar problem with the AC head unit in my 1990 truck. I
believe that the system was still used in the 1992 model with the
addition of a recalculating mode button.

Do all of the features of the AC climate control selector seem to work?
In other words, does the screen show some movement of the indicator
between the icons? If this is the case, the control unit may be working
properly, but there may be trouble with the electrical connection.

To access the AC control on my truck, I needed to take out four screws
to remove the plastic surround covering the edges of the dashboard.
After this, there were a couple of screws holding the AC head unit into
the dash. After removing these screws, the AC control could be pulled
out of the dash and I could access the clip which connected it to the
wiring harness.

It was corrosion in this connection which caused a number of problems
(no hot/cold temperature control, no control of air flow, inability to
select the AC mode, etc.) with the AC control on my truck. Unplugging
and re-plugging the electrical connection solved my problem and it
might solve yours. Using a no-residue contact spray is also beneficial.
At this point, you can test out the system before re-installing the AC
control.

Hope this helps.

PS: I also traced some mysterious problems with the stereo to its
connections to the wiring harness. The stereo on the 1990 truck
contained three components: The tuner, the equalizer/cassette and the
under dash amplifier which was behind the ash tray. Unplug, clean and
re-plug all of the stereo connections and this should fix things.