Audi A6 Fan Problem: Troubleshooting & Repair

Hello.

It's a 1999 Audi A6 2.7 T Quattro sedan belonging to a friend.
When the air conditioner is turned on, the small electric fan gradually increases from a standstill to its maximum speed over approximately 20 seconds, and then runs at full speed as long as the air conditioner is operating. The fan has already been replaced by a workshop, but this has not resolved the problem.
I'm now trying to troubleshoot the problem. I suspect that either the speed controller (who is responsible for this? the control unit?), a sensor, or the radiator is so dirty that the fan isn't getting enough airflow.
Inside the engine compartment, there's a viscous fan and another electric fan (which, in this case, is NOT running; I assume it's a backup fan for the coolant). As mentioned, this fan is located outside, in front of the air conditioning condenser, and it's running at maximum speed, which is annoying and shouldn't be happening.

Furthermore, the outside temperature display on the dashboard is not showing the correct temperature; could there be a connection?

Has anyone else experienced a similar problem? And what do you think of my suggestions for solving it?

Thank you very much.

Hi.

Fans running at full speed and temperature readings that are inaccurate are often related.

Because if the car thinks it's 70 degrees outside, it's clear that it wants to turn on the air conditioning.

m;

It says it's -15°C.

Oops.

"Cooling down" isn't really the right term here, but this temperature is definitely nonsense and could have all sorts of consequences (due to incorrect settings).

m;

Are you aware that the radiator fan must always run at its lowest speed when the air conditioning is on ? Or have I misunderstood you ?

Roger wrote:

Are you aware that the radiator fan must always run at a low speed when the air conditioning is in operation? Or have I misunderstood you?

Sure, the problem is that it's always running at full speed, that it *has* to run, I understand that, but it's running at maximum speed, like a turbine, and that's the problem.
The factory technician replaced it because it makes a noise, but it makes that noise because it spins so fast.

Okay, then all that's left to do is check the error memory and, of course, the outside temperature sensor. The -15 degrees Celsius indicates a defect or a poor connection.

Congratulations on the workshop, by the way. They are replacing the only part that is definitely working .

Quote:

I understand that he HAS to run, but he's running at maximum speed, like a turbine, and that's the problem. The factory technician replaced it because it makes a noise, but it makes that noise because it spins so fast.

"Silly question, but was the fan ever quieter? For me, an A6 with fairly loud fan noise for the air conditioning is actually "normal"."

Furthermore, persistent and implausible temperature readings (e.g., always -15°C) may potentially trigger emergency or protective functions.

Hello,

For an A6 model year 1999, it should be as follows:

Since the 'large' fan is controlled by a viscous coupling, the 'small' fan is directly controlled by the Climatronic system and is not related to the coolant temperature.
The refrigerant pressure switch is also connected to the climate control unit.
The climate control system switches the fan on in two stages, depending on the refrigerant pressure.

If the fan is now running continuously (the two speeds are controlled by two relays, so 'classically' without speed regulation), then either the refrigerant has been lost, or the pressure switch is defective.
In the most extreme case, the climate control system could fail, but this is quite unlikely.

Whoever replaces a relay-controlled fan, when it is working perfectly fine, probably wants to make money or must want to make money.

Best regards, Jochen.