A/C - Windows Fogging Up

91bmw01

Group 64 Heating and Air Conditioning


Bulletin Number 64 17 88 (1776) Page 1 of 2


Woodcliff Lake, NJ January 1991 Service Engineering


This Service Information Bulletin supersedes S.I. 64 17 88 (1776) dated December 1988. It contains additional information concerning causes of the complaint.

Please remove and discard S.I. 64 17 88 (1776) dated December 1988 from your S.I. binder.

SUBJECT: Fogging Up of Windows

MODELS: All

Situations: Under certain conditions a customer may complain that all of the windows start to fog up when entering the vehicle after exercising (skiing, jogging, etc.) or, if several passengers are in the vehicle.

These complaints generally increase in number during the winter months.

Attempts to alleviate this condition by pressing the defroster button (E32/E34) or move the defroster lever to the open position (E30) may only be moderately successful.

This condition can only be avoided if the causes are known.

Cause: Windows fog up when warm moist air in the cabin contacts cold window glass, and the moisture condenses on the windows. Windows may fog up more quickly if the air conditioning system has just been shut off, as condensation remains on the evaporator.

Remedy: Depress the A/C (snowflake) button. This will dehumidify the air, clearing the windows. (This button can be left depressed at all times if so desired.)

When the A/C button is depressed, the cooled and dehumidified air stream is forced through the heater core and reheated as required via the temperature control wheel setting.

Note: Sales Personnel are requested to explain this to the customer upon delivery of the car.


Notes: In addition to the water vapor in the interior due to perspiration and respiration of the occupants, the following adddional sources of moisture must be considered:

^ Rain/Snow: Air that is drawn in is already saturated before it enters the vehicle, making rapid dehumidification more difficult.

Snow can be tracked into the vehicle, and the accessory velour floor mats can hold the resultant moisture for several days. Removal and drying of the floor mats will reduce considerably this source of moisture.

^ Water entering the cabin: Check for possible causes such as A/C drainage, sliding roof drainage, sealing plugs, etc.

The fogging up of windows can be aggravated by dirty windows. If the windows are dirty on the inside, a milky film will form. This film can act like a sponge, attracting moisture to the windows.

The customer should be advised to regularly clean the windows using BMW Cleaner, P/N 82 14 9 400 349 or 82 14 9 406 684.

Warranty
Status: Information only.