I repaired a specific problem, the pressure sensor bias coming from the climate control module(CCM) was too high. The fix for this involves opening the CCM and replacing a component. Not too bad if you have the soldering tools, otherwise an audio repair shop could to it for you. I'LL post more details on this if you need them. However, if the bias level is too low, you may have other problems. Either way, one quick fix is to cut the wire near the sensor and supply a 5V bias from a homemade regulator harness. This will get the sensor bias back to where it should be and give you the use of the AC while you try to find the root cause of the problem (probably a faulty CCM). I fixed mine this way and used it for quite a while before actually going into the CCM and finding/repairing the problem(a faulty 5V regulator). As I said, the bias should be 5V +/- very little. If you are sure the bias voltage to the pressure sensor is causing problems, I can provide more details on how to put together a 5V regulator harness. With basic soldering capabilities and parts from local auto parts/electronics stores, it's pretty easy to do.
Good Luck, Dan

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2012 E350 Bluetech