Expert: Roland Finston - 7/13/2011

Question
QUESTION: I have a 93' Chrysler Concorde in which the display for the
automatic AC / Heater control assembly has gone dark.  The buttons no longer work and the blower runs all the time.  All fuses are ok.  I am wondering if the problem lies in the unit itself or the relay that plugs into the back of the unit.  In talking with my local Chrysler dealer, they couldn't find a relay in their schematic for the unit but then said that I would probably need to replace the entire unit.  I can find a used one for 100.00 but their new one would cost 700.00!

Any thoughts would be helpful.

ANSWER: Hi Andrew,
I would recommend that you look closely at fuse #6 in the fuse box behind the cap on the left end of the dash (10 amp). It might have a subtle crack in its wire. That fuse powers the control unit via a white wire on pin 5 of the black plug on the rear of the unit. That pin should show 12v when the key is in the 'run' position.  
Also make sure that the black/light green wire on pin 6 of the black plug at the rear of the ATC unit shows that to be shorted to ground as that ground wire would be needed to complete the power circuit for the control unit.
Roland
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---------- FOLLOW-UP ----------

QUESTION: Hello Roland,

Thank you for your information, I appreciate it!  In checking the voltage on pin 5, it does show a reading of 12 volts and the ground on pin 6 also is working.  Any thoughts?

Andrew

Answer
Hi Andrew,
There are a couple of other power wires to the controller that you can check:
black/pink on pin 1 of the green plug is a 12v supply but it appears to be only for the rear window defroster grid. It comes from a fusible link and is direct from the battery, but I don't believe it has to do with the operation of the controller proper.
orange wire on pin 1 of the black plug is the headlamp switched dimmable illumination voltage.
But these are long shots. Other than that, with all voltage supplies present but no sign of action, about the only other thing to do would be to open up the control unit and look for any failed electrolytic capacitors that you might replace and thus restore the function. Those usually leak and produce a noticeable sheen on the circuit board when they fail.
Roland
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