Chrysler Repair: Random high defroster heat issue: 94 New Yorker

Question
QUESTION: Hi Roland,
I am a proud owner of my dad's 1994 Chrysler NewYorker, it has a 6 cylinder 3.5 l engine. Almost every time the car is driven the air temperature will go to high heat on defrost and after a period of time back to normal air temperature control although you will manually need to switch the air distribution back to leg or chest air setting or wherever it was previously set. The car has electronic air temperature control. Has been doing this for 2-3 months, was tolerable in the winter but a pain in the warmer months. The problem can last a few minutes or several minutes. It seems to do it more when the car is first started. Please advise trouble shooting,
Thanks so much,
Ed in Maine

ANSWER: Hi Edward,
Use the on-board self-diagnostic capability to see if the unit has recognized a problem and a possible cause. With the engine running but the car at rest, simultaneously press and hold the floor, mix, and defrost buttons (first, second and fourth buttons of the top row). The unit will begin to blink at which point release the buttons. The blinking continues until the unit does a calibration and fault code determination. At that point a number will replace the temp reading (numbers range from 23 to 36). After the first number appears check for additional numbers by pressing the panel button and releasing it. Let me know the numbers you get.
For clarification, does the unit always initiate in the defrost mode regardless of where it was when last driven? Also, does the ac compressor come on (or not) which is the usual action when you ask for defrost? Does the compressor come on when AC is requested in any mode?
Please read the PS (below) and respond to it.
Thanks,
Roland

---------- FOLLOW-UP ----------

QUESTION: Good morning Roland,
I attempted the self diagnostic test this morning on the car before my wife took it to work but it did not work? Held the first second and forth buttons for approximately 10-20 seconds but it did nothing?
If it had, the next step was to press the panel button, which button is the panel button, the auto button or the on/off perhaps?

For clarification when the problem occurs it always goes to defrost and high heat and there is no way to stop it. It eventually stops on it's own and you must then put the air direction back to where you want it. As far as the compressor coming on I have not opened the hood to see if it is running when the problem occurs. Except during the problem of high heat and defrost the compressor works properly.
Thanks,
Ed

Answer
Hi Edward,
I assume the engine was running and you simultaneously pressed the 1,3,4 buttons, at the same time.  Try it again, only this time wait to do it until after the unit has begun to run properly. That may then initiate the calibration and fault code readout.
If it does, after you get the first code press the first button on the bottom row to learn if there is another code as well.
If the display didn't start to blink then perhaps there is an issue with an intermittent fuse that supplies power to the unit.
As for that possible fuse issue look at #6 in the fuse box behind the left end cap to see if it might have a crack in its internal wire.
Let me know what you learn.
Thanks for the rating and nomination. You are welcome to do both again if you would be so kind.
Roland