QuestionQUESTION: I have a 2002 300M, 3.6L engine. Recently the heat/AC digital display started coming on/off and now it is off completely meaning I don't know what the temp inside I chose or if the AC is on until the air is cold or where I have chosen the location ie feet and window etc. I removed the front cover and saw 4 small bulbs, 3 were lit up. I removed the one not lit and it looked like I should replace it so will order a couple. If this doesn't work then what? I don't think it is a wiring problem, when I disconnect the wire plug the heater runs full blast and when I plug it back it I can control it with my buttons, still not knowing what I temp I have.
ANSWER: Hi Punky,
The display in the unit may be faulty or the circuitry on the main board that powers the display function may be faulty. About the only thing to look for as a repair would be the components on the circuit boards that are most likely to fail which are the electrolytic capacitors which are the black cylindrically-shaped components that sit upright. When they fail they leak a solution on to the circuit board and leave a trace of this as a dried marking. If you see any such dry marks around an electrolytic then I would remove it from the board with a soldering pencil, read the markings on the side of the electrolytic and go to an electronic parts store for a replacement and then solder the new one in its place.
Other than that, I suspect you will want to find a used unit in a wrecking yard. I doubt that a bulb being out will resolve the problem.
Roland
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QUESTION: When I took off the front panel, behind it was a round part that also plugged in but I didn't notice any circuit board. If I call a wrecking yard what should I ask for? the entire front panel that would plug into my wiring? thanks Punky
AnswerYou probably didn't take it apart far enough to see the circuit board. But the only part that you are likely to want to buy is the entire ATC Digital Control Box as a unit because that is how it is sold as a repair part.
Thanks for the rating and nomination, Punky. I have one other idea to consider: because the display is able to be adjusted in brightness level it may be the case that the voltage signal to tell the display to light up is missing due to a loose solder joint where the pin for that wire in the socket on the back of the unit is located. You will see an orange wire on pin 4 of the plug which should show voltage of somewhere in the range of 6 to 12v when you turn on the unit (depending upon whether or not you have the headlights on). So check for that. If you show a voltage then you could open the unit and notice where the pin on the socket for that wire attaches to the circuit board, and heat up that solder joint with a pencil just on the chance that it might have become disattached and heating up the solder would fix that.
