Originally Posted by Turbonut

As there are many components involved, driver's and passenger's mode control motor, driver's and passenger's air mix control motor, plus other sensors and transistors, might want to try a self diagnostic test to see if any DTC appear.

Turn ignition on
Press and hold the OFF button. While holding the OFF button, press the circulation button 5 times within 10 seconds. Release the OFF button and the self-diagnostic will begin.

If there are any problems in the system, the temperature indicator will light up the segment of (A through S) corresponding to the error. The temperature indicator will then alternate every second between displaying "88" (all segments lit) and error code (A through S). To determine the meaning of the code you'll need to the DTC troubleshooting index.

If there is no problem detected, the segments will not illuminate.

Turn off the ignition switch to cancel the test.

Each part of the "88" indicates, or translates to a specific letter, e.g. top of the first 8 on the driver's side is a C, top of second is a D, passenger side temp, top of first 8 is a L, etc. and each segment indicates a specific problem.

Don't have a scanner so can't load the detection code values, but just as an example, if the top of the first 8 is lit, that would translate to a C:

C-An open in the outside air temperature sensor circuit.

At least you can see if there are any codes to indicate a problem within the system.