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I just noticed my fan goes on right after I start my car even tho my engine hasnt warmed up yet. What could be the underlying cause or problem
 

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doesn't the fan run anytime the AC compressor is on? or am i incorrect in that?
 

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I think the fan is triggered by the DME according to radiator outlet temperature and AC pressure. It doesn't neccessarily mean it'll always run with AC on.
 

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E30M3 Race F10 535 R1150Rt M Coupe
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I think the fan is triggered by the DME according to radiator outlet temperature and AC pressure. It doesn't neccessarily mean it'll always run with AC on.
Correct. Insofar as when the fan comes on. A: It's in stages. B: The stage (on or not) is dependent upon the system pressure in the A/C system and/or the radiator coolant outlet temperature. Both instances of coolant outlet temperature and A/C system pressure can be present at the same time. Whichever value is greater (demanding the most fan intervention) will be the dominant one until it's satisfied than the lower threshold takes over.

Example: You're returning to the car in a parking lot after 5 minutes. Engine was already warmed up. The car is hot and you want everything the A/C system has.
Starting the car and going full A/C could see two things happen:
The A/C system pressure raises significantly (High value) AND the hot coolant has just exited the block and the temp sensor @ the bottom of the radiator is activated. (usually a lower value than HOT car & full A/C.)
The DME needs to drop the pressure of the A/C system fast, the fan will ramp up to a higher stage. Then will lower and the "high demand" is satisfied for a bit. At the same time the DME sees that the coolant outlet is still a little high (it did benefit some from the fan running for the A/C system) and needs a little more. Now the lower threshold for the coolant outlet will usually see the fan run at a lower stage until that's satisfied and/or the A/C system pressure again asks for some more.

Make sense?
 

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There's older K-CAN protocol and newer faster D-CAN. K+DCAN simply means the cable supports both. E46 uses K-CAN so it should work.
 

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I had the same issue, it turned out it was a fault with the AUC sensor causing the AC pressure sensor value to be clamped high, in turn causing the AC fan to turn on.

Try unplug the auc sensor and see if it fixes your problem.
 
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