A/T - Microfilter Replacement Intervals

9225bmw01

Group 64
Heating and Air Conditioning


Bulletin Number
64 06 92 (3518)


Woodcliff Lake, NJ
March 1992
Product Engineering


SUBJECT:
Microfilter Replacement Intervals

Complaint:
Reduced air flow at low blower speed, so that the microfilter must be - replaced before the scheduled replacement interval.

Cause:
In vehicles, which are primarily operated in the city or industrial areas, it may be that the microfilter has to be replaced prior to inspection I. This is the result of heavy air pollution.


Air pollution in the above mentioned areas will normally consist of microparticles in a size spectrum of 0.001 to 5 micro.


General
Information:
The microfilter is designed to trap these potentially irritating types of particles with very high efficiency.





The pore width of 3 micro is a compromise between acceptable penetration of pollutants (refer to diagram) and a slightly reduced air flow rate.


Under normal operating conditions the microfilter must be replaced every Inspection (I and II). This is equivalent to vehicle performance of about 10,000 to 15,000 miles. Beyond this mileage, the air flow rate will be slightly reduced in all blower speeds due to the contamination build-up on the microfilter.

The actual service life of the microfilter depends on the above mentioned air pollution and an acceptable air flow rate reduction.