Climate Control Issue
 

Recently, my e60 climate control is acting up, not all the times just occasionally. The symptom is that: after AC is "settle down" (no more high fan speed/loud fan motor noise), it runs very quiet and keep car compartment cool and dry. Then all of a sudden, fan motor speed up and "mold" smell comes out from vents. It feels like AC gotten turned off. Fan motor keeps on running at high speed and it may or may not goes back to "normal" (low speed). I have to turn off the auto AC and then turn it back on to fix this issue.

Any suggestion about the cause of the problem ? Car's AC system is still "original", have not been serviced so far after 110k miles and about 11 years of usage.

Thanks