Slide the radio all the way out & let it hang by the wires. Click here for the link for removing the radio.
The top dash grill has 2 phillips screws holding it in place. Press the 4 clips in the corners to slide the center vent assembly out. You can reach the ones on the left easily, the bottom right hand one is tucked behind the OBC but once the left side is tilted out, then pushing the top right clip down will let the whole thing come out easily. Details may be different right-hand drive. The thumbwheel light bulb is BMW part no. 07 50 9 063 579. It is the small wheat lamp style & costs 90 cents.
If only replacing the bulb, it can be removed by just removing the top grill, but it is extremely difficult to get the bulb holder back into the hole. If you have the vent removed for other reasons, install the light before pushing the vent back into place.
If the vertical vanes are loose, use a toothpick to put a small amount of Loctite #242 (medium strength) on the crossbar journal of the middle vane, the one with the integrated thumb lever. It will set up after about a day & be frozen for the first adjustment attempt, but the bond breaks easily & now it will have the right amount of friction to hold the vanes in position with higher fan speed settings.
If the foam has deteriorated, you can get self-stick weather stripping foam at most hardware & home supply stores, get one 3/16" x 3/4" or cut down a wider one, 1/4" thick foam is a tight squeeze when re-installing the vent assembly.
Sometimes the potentiometer traces in the center thumbwheel will get dirty & have a higher resistance. This can sometimes cause less warm/hot air flow thru the center vents in the winter, but is not always the culprit. The center vent will come completely out once the connector is unplugged from the wire harness. It's burried behind a large wire bundle immediately behind the right corner of the instrument cluster. The wire coming from the center vent is about 12" long & the plug can be unplugged by reaching thru the top center grill cavity.
The potentiometer is integrated into the center vent assembly & I could not find a way to remove it from the housing without breaking something, so I sprayed some contact cleaner into the back side & worked the thumbwheel back & forth a few dozen times. The resistance measurements ranged from 2.27 k-ohms to 4.65 k-ohms before spraying & dropped to .218 to .670 k-ohms after cleaning, but once it dried, the resistance jumped right back up to the 2 k-ohm to 3 k-ohm range. New replacements come only as a complete unit from BMW & cost approx. $150.
Results from cleaning the potentiometer provided no difference in the center vent hot air performance.
gale, 92 735i
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