AC controls not working...

[nebilex]

The AC control unit stopped working a few weeks ago, i figured it would be the fuse so i checked that first and f48 was toast. I changed it and everything was working fine until a couple of days ago when the controls stopped working again. Unfortunately i am traveling until monday so wont get a chance to look at it until i get back. I asked a friend to check the fuse so the wife can drive the car. My question to he experts here :-) what is causing the fuse to blow within two weeks? Is it the blower motor resistor causing this?

[Zulu95]

I remember reading about the fans behind the little grills on the head unit for the cabin temperature sensors getting dirty, gumming up and then blowing fuses. a blow out with canned air should free them up. A search may turn up what I read.
GL

[nebilex]

Thanks Zulu, unfortunately I couldn't find the discussion you mentioned. I searched bimmer forums etc.. as well

Anyway I decided to post my findings and will post my fix whenever i figure it out:




There is actually a service bulliten for this issue.


SI B 64 08 06
Heating and Air Conditioning SystemMay 2006
Technical Service
This bulletin replaces S.M. B64 201 03 dated July 2003.

SUBJECT
IHKA Inoperative Fuse 48 Blown

MODEL
E53


SITUATION
The IHKA (Automatic Heating Air Conditioning System) functions intermittently and the control panel display blanks out. The temperature settings may also change automatically. Eventually the IHKA cannot be operated anymore.

CAUSE

1. Pinched or chafed M-Bus wiring harness
2. Fuse 48 blown, caused by short in wiring harness

PROCEDURE
Check the following areas for problems:

1. for a pinched wiring harness, especially in the driver's side knee pad area between the instrument panel carrier and the IHKA housing.
2. Inspect the wiring harness for any chafing damage, especially from the sharp edges of the instrument panel in the glove box area.
3. Check for wiring shorts in the area of the water valve assembly.
4. Inspect the wiring at the auxiliary water pump, especially in the area of the frame rails.
5. If fuse 48 keeps blowing, check the wiring between fuse 48 and the IHKA control panel for shorts.
6. If any damage is found in the wiring, repair the wiring and reposition the harness away from the affected area. Edge protectors can be installed to ensure the wiring is not damaged in the future. The edge protector can be ordered in a unit of 1 meter and can be cut into the appropriate length.
7. If wiring has no shorts and Fuse 48 is not blown, check power supply and ground at the IHKA control module. Ensure pins are not loose at IHKA module