A6 C4 AC Fan: Troubleshooting & Repair Guide

Hello,

A phenomenon that has been bothering me repeatedly for about 2 years is the following:
A6 C4 model '96 with automatic climate control. When manually adjusting the fan speed, I observe that the fan speed does not increase when the top 2 or 3 bars are displayed on the screen.

To which error can this effect most likely be attributed?
Are the carbon brushes in the fan motor worn out or dirty, or is that the cause?

Best regards, Kai.

Use a multimeter to measure the voltage directly at the fan motor. At full power, you should see approximately the vehicle's battery voltage, which is 12-14V. At half fan speed, you should see around 6 volts.
If the voltage drops below 11V at full power, check the positive and ground wires, as well as the electronic pre-resistor, which is usually connected to ground. Verify the ground and positive voltage. If the voltage is okay, measure the voltage from the Climatronic control voltage to the electronic pre-resistor (thin cable). I don't know the target values, but the voltage should increase with each higher setting. All values should be measured with the engine running and a minimum of 13 volts.
Did you also check if the pollen filter is clean?

Hi,
I would also check the pollen filter first. Dead fans often start making a terrible squealing noise. And taking it out is a real pain.

Best regards from Berlin.
olli

HI,

I replaced the pollen filter this year, but the problem is still there. I'll measure the voltages soon, if the pinout is clear in the wiring diagram. Best regards, Kai.

Hello,

The error hasn't been investigated further yet, but it's not critical, and the ventilation system is still working.

'But I have one more tip that might help one of you pinpoint the error before I have to start searching for the cables and find places to take measurements.'

I tried to read the OBD diagnostic data using the climate control system:
Channel 18: Actual value of fresh air blower voltage.
Channel 19: Setpoint for fresh air blower voltage.

'When I slowly increase the fan speeds on the climate control system and read the values of both channels intermittently, I observe that the target value increases up to 12.5 (the maximum value), but the actual value remains at around 9.'

Where does the Climatronic system get the actual temperature reading? Does it receive it from the fan, or does it measure it using its own dedicated output port?

Best regards, Kai.