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Old 11-19-2011, 05:48 AM
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joyism5 joyism5 is offline
Officially Welcomed to the 'Fest
Location: USA
Join Date: Jan 2011
Posts: 1,271
Mein Auto: '99 740IL, K75RT
Did any of you guys had the fresh air filters and cabin air filters changed?
They are 4, 2fresh air filters on the hood, and 2 cabin filters (under the dashboard one on driver side and one on pass. side). It is essential to have filters change every year or 15k miles depending on the dusty driving conditions. Lift the hood, and on the firewall there are 2 door flaps for the air duct. Push the doors and check for debris or strange object in there.

Microfilters are used in BMW climate control systems, this includes all vehicles produced
after 9/91 (except E30) .In addition, all E31 vehicles have been equipped with microfilters
since start of production.

Fresh air is continuously filtered through the microfilters. Never operate an E38 without the microfilters installed,
There is the danger of water being drawn into the heater and/ or damage to the electrical

The microfilter is designed to trap potentially iritating types of particles with very high efficiency.
Examples :
-Floating air pollution

Under normal operating conditions the microfilter(s) should be replaced every Inspection I
and II (also every Oil Service 99 MY), except for M roadster or M coupe.The actual
service life of the microfilter depends on the amount of contaminant and air flow rate
reduction complaint, therefore the replacement interval may be more frequent in dusty
operating conditions.
E38 models have additional filters for the recirculation air inlets which require replacement
at every second inspection II.

Now, while you are changing the filters , check the air duct for leaves or an kind of dirt. If that doesn't solve the issue you might have a door flap actuator problem or the AC control panel. More info about the air distribution in these cars :
Microfilter replacement :
For those that the defrost is not working at all , the defrost button should be removed and check the OHM resistance with a voltmeter, like described here If there is no resistance at all , this might pin point an door flap actuator failed.

Last edited by joyism5; 11-19-2011 at 05:56 AM.
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