QuestionQUESTION: I have a 1994 Chrysler LHS with the ATC. It seems that the temp control does not put out enough heat (about 120 degrees) when set to max (90 degrees) in the override mode, which is not enough to heat the car. Does the thermistor function in the manual mode as well as the auto mode or is there something else which controls or affects the temp. The heater core is not blocked and the engine temp is normal
ANSWER: Hi Jan,
Here is how I have answered similar questions previously:
The unit does have a self-diagnostic capability. The engine has to be running and the car not in motion to do the test. Simultaneously press the floor, mix, and defrost buttons, (the 1st,2nd and 4th on the top row) and see if the display unit begins to blink. Release the buttons when it has started to do that and then after it blinks for a while longer watch for two digit numbers to appear on the readout. Those are the fault codes. If the first number appears and stays in place, push on the first button in the bottom row (panel) to continue the readout. At the end of the readout the unit will return to normal settings.
Then write back with the number(s) and also tell me more about exactly what is wrong with the function of the unit.*
If the head unit doesn't respond at all, then check fuse #6 under the dash. There is also a 12V supply line to the control that is directly connected to the battery on a black/pink wire on the green plug on the rear of the control unit that should be checked to verify that you are getting that power to the control unit.
I would do a thorough readout before buying a new control unit. It may be a part in the air distribution system itself rather than the computer that is the problem. And you also might find a working used unit at a wrecking yard.
Roland
*The code numbers range from 23-36. You can also get a decoder list at www.allpar.com/fix/codes_climate.html
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QUESTION: I have been through all the tests. I don't get any error codes. I wonder how the thermistor sensor behind the dash affects the temp?
AnswerHi Jan,
According to the '94 manual, if the sensor is open or shorted then the digital system turns off and the unit defaults to manual operation.
Is the aspirator motor working to pull air over the sensor? To check the motor, turn the ignition on, then turn off the ATC control to stop any ventilation air from circulating. Then hold a piece of tissue paper in front of the grille and see if it sucked inward or not. The aspirator motor functions even though the ATC is off, so long as the ignition switch is in the 'on' position. Also there are a couple of foam seals that are needed to assure that the air flow is proper over the sensor. One is on the inside surface of the trim bezel directly behind the name plate. The other is a seal (strip) directly to the right of the right center duct opening (this is a direct quote from the manual). To gain access for inspection you remove the right end cap from the dash panel (open the door to to that). Remove the right trim bezel from the panel (there is a screw at the right end which was hidden by the end cap which you should remove) and then you can pull the bezel off because the only other thing that holds it in place is friction. You can then inspect the sensor/aspirator/seals, I would believe.
Roland
