I ma having the same issue, however I had a friend of mine take a look at it. He's a BMW mechanic. to get to the evaporator, you will have to remove the entire dashboard. the evaporator is at the fire wall. go to the OEM site for bmw (real oem) enter your model information or the last seven of your vin. and look for the part there. it show you were it goes.
if you find out nay other helpfull hints or help on this, please share it with me as I ma having the same issue.