QuestionThe display of the digital HVAC Control is blank on my 1987 Chrysler New Yorker and the heater and A/C will not turn on. I replaced the control with a new unit and it still does not work. The lights around the buttons are powered when the headlights are turned on so I know the unit is getting power. The blower motor is getting 12v power on both wires. The after market book that I have does not have the wiring diagram for this part of the vehicle. What should I check for next? Where can I find the wiring diagram for the HVAC system?
AnswerHi D harris,
I have the 87 wiring diagrams for the New Yorker ATC system and I must say it is less than perfect, in that not all the plugs are described and the various units are treated as black boxes so you really can't understand completely. For example you said that the blower motor is getting 12v on both wires which of course means that it won't operate. One of those wires has to be grounded for the motor to turn. But the wire that is the one that needs to be grounded goes to a two wire plug at the part of the ATC unit that is called the power/vacuum module but what happens inside the module is unknown. The wire is an "H" code, which means it is part of the ground circuit, but it must be a wire that is switched to ground by the module in order to make the motor run (because you say it not has 12V on it). But I believe that the issue is not the wiring, but rather in the unit itself, specifically the power/vacuum module.
Let me give you a few pin assignments for the 13-pin blue plug on the control unit so that you can test them for voltage.
The 13 pin plug:
pin 1 yellow trace is the "display set up
signal from the headlamp switch"
pin 3 black/light green is electronics ground
pin 4 white is igniton/accessory run feed to electronics
pin 7 red is battery feed for the memory
The power for the unit comes from fuse #4 (30 amp) and is split, one lead to the blower motor (dark blue) the other llead goes to the power module (which is part of the multisided module at the far right hand end of the ATC unit, that part which has three plugs, with 1,2, and 3 wires each. You should see a dark blue power wire at the 3 wire plug). I suspect that the power module is the source of your problem because that is where the 12V main supply line goes to, but the diagrams are too opaque to understand exactly what the function of each of the other wires at that module are. I would suggest that you try to find an '87 vehicle (Plymouth Caravelle, Dodge 600, Chrysler New Yorker, J and K Body LeBaron) in a wrecking yard that has the ATC unit and buy the power/vacuum module. The wiring is different in the '89 models and I can't speak to the 86 or 88 models. There was no 85 ATC as far as I can tell. I believe that power module in your car is broken, but there are no internal diagrams for it. You could examine the circuit boards to see if you can find a capacitor that has leaked fluid which shows it is blown and replace that to see if you can resurrect the power module that way.
All the other trouble shooting feature of the control unit depend upon the digital display being lit, and are unrelated to your problem which appears to be a power supply (power module) issue.
Let me know what you learn.
Roland
