I found this for a 97 searching google
Press and hold the Floor + MIX (Floor/Defrost) + Defrost buttons until the
display begins to flash.
The HVAC doors will begin to re-calibrate themselves.
After a minute or so the flashing will stop. If there are no fault codes
the system will return to the previous temperature seting, otherwise the
first fault code will be displayed. Press the Panel button to get other
fault codes.
This for a 94:
do this set the control to 75 degrees. To diagnostic mode press and hold
the floor, mix and defrost buttons at the same time. The ATC head display
will begin to blink, when it blinks release the three buttons. Once the
control head enters diagnostic mode, the display on the control head will
continue to blink. This occurs until it completes its tests and
calibrations. It goes crazy so don't worry, all the vents and heat and ac
go nuts during this. The dispaly will read out and trouble codes if there
are none the system will return to normal operation. here are the codes:
23 ATC Blend Door Feedback Failure
24 ATC Mode Door Feedback Failure
25 Ambient Sensor
26 ATC In-Car Sensor
27 Sun Sensor Failure
31 ATC Recirculation Door Stall Failure
32 ATC Blend Door Stall Failure
33 ATC Mode Door Stall Failure
34 Engine Temperature Message not Received
35 Evaporator Sensor Failure
36 ATC Head Communication Failure
