By any chance, did you have the battery disconnected recently? Take a look at this TSB.
1991 Chevy Truck K 1500 Truck 4WD V8-350 5.7L
HVAC Control Head - Inoperative, No Display
Vehicle Heating and Air Conditioning Control Assembly Technical Service Bulletins HVAC Control Head - Inoperative, No Display
HVAC CONTROL HEAD - INOPERATIVE, NO DISPLAY
Date: NOV. 1992
Corporate Bulletin No.: 261210
ASE No.: A7
HEATER VENTILATION AIR CONDITIONING (HVAC) CONTROL HEAD INOPERATIVE - NO DISPLAY
Model and Year:
1990-93 C/K TRUCKS
The HVAC control head on some 1990-93 model year C/K trucks may not illuminate when the vehicle is first started. This condition is much more likely to occur after a battery disconnect or control head replacement but may occur after any ignition cycle.
The condition is not permanent, it stems from the control head not receiving a correct signal when the ignition is turned on.
Recycling the ignition switch may bring the control head back to normal operation. If cycling the ignition does not work, disconnect and reconnect the battery making sure that a good electrical connection is maintained when reconnecting (avoid "chattering" the battery line).
If that isn't the case, I need you to check for power to the control head. See pic 3 for the power supply. Also, pics 1 and 2 are relevant to the power supply (fuse). Reconfirm the fuse is good. If it is, confirm there is power in and out of the fuse.
Here are a few links you may find helpful:
Let me know what you find.
Images (Click to enlarge)
Friday, April 30th, 2021 AT 4:13 PM