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Old 07-15-2009, 02:55 PM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
With the summer in full swing, the AC stink problem arises again.

With another year under our belts, is this the recommended set of ac-stink problem statements and recommended solutions?

- It's first, and foremost, a BMW A/C downsize design problem (too cramped for proper ventilation of evaporator coils)
- The design problem allows food (dust), water (evaporator coils & ducts) and microbes (stinky poo) to coexist
- Resolution entails design, maintenance, & behavioral modifications (reduce the water, food, and stinky microbes)

DESIGN MODIFICATIONS: (Note: These are draconian)
- Cut hole in driver right-foot panel so you can spray germicide directly on evaporator coils (kill the stinky microbes)
- Drill a larger hole &
clean the evaporator fins with a toothbrush (less food for the stinky microbes)
Unkink the E39 evaporator duct (behind dash) by wiring the damper (less water for the stinky microbes)

MAINTENANCE MODIFICATIONS: (Note: These are judicious)
0. Reseat the two cabin-air micro-filters in the engine bay (BMW says stink can get in if they're not seated well)
1. Check if there is water normally draining from under the car after running your AC on a hot day
If there's no water pooling on both sides of your parking spot ... then ...
2. Clear the two undercarriage drain tubes any way you can:
- Some people suggest you snake a coat hanger past the multiple elbows to the evaporator coils to unclog
- Probably more reliable is to attach 13.5mm to 14.0mm OD plastic tube to both drain hoses & blow out obstructions
3. Unclog the drain holes & tubes in the two engine bay micro filters
- Some suggest snaking a six-inch length of coat hanger into the holes from the cabin filter downward thru the rubber drain hose
And, for more serious cases of BMW stinky AC:
4. Replace both engine-bay cabin "micro" filters (less food for the stinky microbes)
If eliminating water has been done, yet the stinky-AC microbes are still active ...
5. Spray tons of disinfectant in the air intake or directly onto the evaporator (through the drilled hole method).
- You'll need tons of germicide because it's not a direct shot to the evaporator coils from the air intakes
- Or try somehow to spray germicide upward hopefully onto evaporator coils from the undercarriage drain tubes
- While you're at it, spray ample germicide in central cabin vents (hoping some germicide lands on evaporator coils)

Note: The undercarriage drain tubes are apparently hard to remove for direct access to the evaporator coils; and, worse yet, they have a 90-degree elbow and 1-foot horizontal run, so, they're difficult to get a coat hanger into and even more difficult to get germicide up far enough to coat the evaporator coils.

BEHAVIORAL MODIFICATIONS: (Note: The fact we have to do this is ludicrous)
- Each trip, turn the AC off five miles before you arrive at your destination (less water for the stinky microbes)
- Park slightly nose upslope presumably so horizontal drain tubes drain better (less water for stinky microbes)
- Once a day, turn the heat up to 90 degrees and cook for 15 minutes (kill the stinky microbes)
- Set the AC to 72 degrees, "Auto", "Snowflake", & "
Circle without the A" (basic setup but doesn't help much)

Note: Yes, it's crazy to own a "luxury BMW" and then have to babysit the AC by turning it off or turning the heat up to 90 degrees in the hot summer so that it doesn't embarrass you with AC stink when you have a customer in the car; but, what else can you do?

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Last edited by bluebee; 07-21-2009 at 06:00 PM. Reason: I'll add suggestions for eliminating the stink as they come in (as long as this will let me edit)
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