Trunk Mounted Fan for Changer/Nav compartment

By Tom McCandless, Sierra Vista, AZ BMW CCA 288126

After returning from Tucson one day this past summer the trunk mounted changer in our 99 528i glitched a few times. So when we got home I decided to change out the CDs in the magazine to see if they were the problem. When I ejected the magazine it was quite warm so I stuck my hand down in the magazine well to see just how hot it was in there. It was HOT! After about a ten minute cool off period with the trunk and compartment open, the changer worked just fine again. Being an electronic tech and well aware of how electronic equipment dislikes heat I decided a little additional airflow was called for. Seems that the only air source for the electronics and battery compartments is whatever air filters through from the cabin area via the trunk and that is only if the cabin pressure is higher than the trunk pressure. There is a one way vent in each compartment to allow air to be sucked out at speed but stopped in downtown Tucson traffic? Nada! And the muffler mounted just under the electronics bay doesn’t help much either!

So I mounted a twelve volt computer case fan on the inside of the compartment door and wired it into a switched twelve volt source. Your wiring color code may be different so make sure you have the right ones before removing the insulation. Mine are Brown with Black stripe for ground and Purple with a White stripe for the switched twelve volts. You can reach the backside of the connector pins with most meter probes so check first.

If you MUST use a knife to remove the insulation, be very careful not to nick the wire strands. All it takes is a nick and a little vibration and you have a broken strand. One reason that I won’t use the clamp on type wire taps and splices is that they can nick or even cut the wire strands. And they don’t make all that good a connection either.

I prefer to use a thermal stripper if at all possible since it’s almost impossible to damage the wire with one. Fortunately my soldering iron heating element is internally threaded with a 3/16 coarse thread. The right size copper wire, threaded, makes dandy tips. So I flattened the wire down to about a millimeter thick, and filed it flat on the ends and sides and put a small notch in the end. Makes a dandy "shade tree" stripper. Basically you just use it to heat the insulation almost to the melting point and scrape it gently off.

Solder the fan wires on, clean off the flux, and insulate the joint. I used "liquid tape". Three or four coats is enough and it dries fast. You can get it at most hardware stores. I put the little two pin connector in the lines to the fan so if I want to remove the compartment door for better access, I won’t also have to remove the fan.

Use the fan grill as a template to cut and drill the holes in the door. I used a Dremel tool with a rotary cutter for both. GO SLOW! You want to cut the plastic, not melt it.

The pictures should tell the rest of the tale.

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Have fun!

Tom McCandless

Sierra Vista, AZ

BMW CCA 288126