A/C - Sudden Temperature Fluctuations

9220bmw01

Group 64
Heating and
Air Conditioning


Bulletin Number
64 07 92 (3519)


Woodcliff Lake, NJ
March 1992
Product Engineering


SUBJECT:
Sudden Temperature Fluctuations in Passenger Compartment

MODELS:
IHKA E31, E32, E34/IHKR E34, E36

Situation:
The temperature in the passenger compartment suddenly drops or raises as much as 10-13 degrees F. The vehicle usually will heat/cool normally after being switched off at least 3 minutes temperature controls will still function normally.

Cause:
A production defect in the outside temperature sensor might cause an occasional short circuit. The control unit considers the sensor faulty and substitutes a value of 32 degrees F. If the temperature outside is much higher or lower than 32 degrees F, the system immediately compensates for the perceived temperature change. The result is a noticeable sudden change in cabin temperature.

A temperature sensor fault is entered into the control unit, however the IHKA control units will erase the fault if the ignition is switched off for more than three minutes.

Correction:
If the above complaint is experienced with a vehicle, or a fault as described is discovered in the control system, replace the outside temperature sensor.

This problem has been fixed in production for 11/91 and later vehicles.

Note:
This problem is not related to a known problem with E36 IHKR systems suddenly losing heat. In that situation all control of temperature is lost, and the only way to obtain heat out of the system is to "override" by moving the driver's temperature control past the detent to maximum heat. The problem in THIS service information occurs as a sudden slight (but noticeable) shift in air temperature, either up or down, that can easily be compensated for by adjusting the teinperature controls.

Due to a number of recent complaints with the automatic air conditioning systems, BMW NA is requesting technicians to fill out a Quality Report or "pink sheet" detailing the symptoms of affected vehicles and the effectiveness of this repair. Your cooperation is greatly appreciated.