QuestionMy 94 Concorde had a defroster that would run sometimes whether we wanted it to or not. Just recently it runs full blast all the time and the environmental control readout is blank.
-Tom
AnswerHi Tom,
I suspect that the ATC head unit is faulty because it doesn't light up and becasue of the loss of control of the air distribution, though it could be a fuse issue also. The blowing continuously may be due to a faulty blower motor module which is located in the air duct to the left of the blower, but I would not conclude that is the problem until the control unit was working once again. The unit does have a self-diagnostic capability. The engine has to be running and the car 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 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. To remove the control unit use a screwdriver tip to pry the bezel edge gently away, then pull straight back on the bezel surround that conceals the radio and the ATC unit. Then remove the 3 screws that hold the ATC control to the dash structure. I know of no service manual for the ATC head unit, but you might inspect the circuit board for sign of a blown capacitor or other component failure which you may be able to replace with parts from an electronic supply. Otherwise, try to obtain a replacement from a pull-it-yourself wrecking yard.
Once you get the head unit going again, then if the blower still is on all the time you need to check the blower module.
This behavior of the blower motor is usually caused by a failure of an electronic module called the blower power module which is unique to the ATC unit. You can get to it by:
Removing the lower right underpanel access cover silencer duct below the glove box. When replacing this make sure the left hand end fits into its recess in the ducting.
Trace a pair of wires from the blower motor to a black 5- wire plug* on the air duct. That is the plug for the module. The module is inside the duct and held there by two screws.
Then remove the module.
If you have some experience with electronic components and a soldering gun you might try troubleshooting the module for repair, look for one in a wrecking yard, or buy a new one from the dealer.
Please let me know how this works out.
Roland
*beside the motor wires there are three wires colored black, light green/red, and dark green.
Roland
