BMW E46 Heater, Air Conditioning (AC) Blower Fan Speed – 323i, 325i, 328i, 330i, M3
car year: 2001
car model: 330ci Convertible
Does my air conditioning fan have more than one speed? We have experienced over 50 days straight of temperatures in the 90s and the fan seems to run only at a high speed, and sounds like a turbine engine. It seems to go directly into this high speed mode even after sitting indoors all night, with morning temperatures only in the 80s. Your thoughts?
First, let’s make sure we understand the operation of the automatic climate control system in the E46 chassis (3-series 99-05).
When in automatic mode (press AUTO button), the word AUTO shows on upper-right of the display and the chosen interior temperature shows at the left of the display. If the interior temperature is above the chosen temperature, the system will go into full cooling (high fan speed, best airflow ducting and maximum cooling) until the desired temperature is reached. It will then reduce the fan speed and cooling in order to maintain this temperature. Naturally, hotter days will require more cooling and more fan speed (air flow). One potential problem, when using the AUTO mode, is debris clogging the air intake grills for the interior temperature sensor. These are the small grills on either side of the climate control display. A small fan draws air through the grills. If the grills and air flow to the temp sensor are clogged, the AUTO system will continue to stay on high, since the sensor is staying hotter than the actual interior air. Use a can of compressed air (available at computer stores and most office supplies) to blow through the grills in an attempt to clean any dust from the system so that the air can flow properly.
The above points also hold true for heating.
Have you tried to run the fan speed manually? Use the fan speed control button (below the display, with the small and large fan emblems) to run the system manually, just as you would in an older car. As you press the left side of the button (small fan emblem) does the graphic display of the fan speed (on right side of the digital display) reduce to smaller bars? If not, the control unit is likely at fault. If it does, does the fan speed reduce? If not, the blower final stage unit is likely at fault. If the fan speed does reduce, all should be OK, and you likely just need to clean the air intake grills for the automatic temp sensor.