Chrysler Repair: 91 Imperial ATC: Heat stuck on high only, soldering pencil, electrolytic capacitors

Question
Hi,
I have a 1991 Chrysler Imperial with a 3.3L and the automatic temp is stuck on high and the LED for the temp or functions does not light up nor can I change temp range no a/c just hi heat coming out do you know what would cause this? No fuses are blown.

Answer
Hi Anthony,
If there is no illumination from the LED panel then see if fuse 9 (and 5 and 14, as well) are all showing continuity (no cracks in their internal wires and certainly not blown), and if OK then I would believe that the control panel is malfunctioning. You could remove it and see if you find any blown electrolytic capacitors on the circuit board or melted resistors, and also test that the connection from pin 2 of the  21-pin socket to the circuit board is patent (reheat the solder if you have a soldering pencil). Also verify that there is 12v on the incoming pin 2 of the plug (white/pink wire) when the ignition switch is in the run position.  Those would be the simple causes for their being no illumination. At that point looking for a replacement control panel would be logical.
If you can get the LED back 'on' then see how it works. If there is still a problem then we can try some self-diagnostics but those depend upon the LED being functional.
Roland