Expert: Roland Finston - 7/14/2011

Question
I have a 2002 Chrysler Sebring 4 cylinder and I'm having problems with the AC unit.  The air conditioning compressor only goes on when the switch in on defrost and not on any of the air conditioning settings.

Is this something that can be fixed fairly cheaply.

Thanks

Answer
Hi Dan,
I haven't heard of that sort of problem before. I don't believe that the ac compressor clutch is going to not be activated due to whether there is a given refrigerant pressure in the system that is different depending upon whether you ask for ac or you ask for defrost. But that is a possibility if you are margial in the refrigerant charge.
Out of curiosity why not see if when you ask for rear defogger the ac compressor activates or not? If it does, then I would believe that the problem is in the control switch proper; if it doesn't then I suspect it is a resistor attached to the switch in the control unit that is part of the sensing process that the body control module is programmed to notice when you have asked for ac or rear defogger. So you would open the controller to check that resistor. You could check to see whether the voltage on pin 5 of the 16-pin plug on the back of the controller changes noticeably when you move the switch to the 3 ac request positions. If so, then the switch is ok. Try measuring also the resistance to ground from that pin when doing the same ac requests compared to any of the other settings, as that may also be the change that the body controller is looking for.
The only other simple possibility is that the wire from pin 5 or the 16-pin plug on the back of the controller (red/tan) to pin 23 of the upper white color plug at the body controller (verify wire color as there are 2 such plugs there) is disconnected/open. That wire is what carries the 'sense' that you have asked for ac/rear defog.
Roland
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