My car begins to overheat when I idle with the AC running. The car has 3 fans:

1. Mechanical fan that runs all the time and increases speed as heat increases due to a viscous coupling.

2. Small electric fan in front of the radiator that runs with AC pressure. It also runs with the afterrun switch when I turn off the ignition.

3. A big electric fan next to the mechanical fan. Mine never runs, but Audi says it's supposed to run in low speed mode when the AC is on. Can anyone confirm that this is true. I think they're trying to get out of checking the car any further.

 

strange set up I would say one fan on the front runs with the AC all the time so why have the other fan sitting there doing nothing, I would say its a booster fan for the coolant while idling to prevent overheating when more electronics are used ( theoreticly they could be right ) but if it dosnt work there is a problem

 

Thanks for the response but I don't want to order anything else on speculation. Can someone please turn on their AC and look to see if the big electric fan inside the engine compartment is running.

 

There are three fansthe one on the inside drivers side spins all the time, the passenger side and front fan started spinning with the A/C.

 

Great, thanks for your time. Does anyone know how this is triggered? I'll check for voltage first to see if the fan is toast, but if it isn't present which switch or sensor triggers this thing.

Audi said it is in low speed mode with AC, then high speed mode if the gauge reaches about 3/4 scale.

 

The fans are controlled for coolant temp by the blue sensor located towards the front of the car in the lower radiator hose. The brain of the system though is the failure prone fan control module located under the hood under the driver side frame rail above the oil filter. I'd take 12v and run it right to the fan see if it runs, also check to make sure there is nothing obstructing the fan, on a lot of a6's and allroads they had a problem with a piece of trim of something wedging in the fan stopping it and burning out the module.

 

I did try the start in question like how does a fan work but I don't want this

I don't want to order anything else on speculation that's an insult to my intelligence

 

Just a thought, but have you tried to bleed the coolant to make sure you don't have a air bubble?

My car only has one fan, & runs fine.

 

No offense, but your response was "theoretical" in your own words. I specifically asked for someone to verify something for me.

 

I blead 2 points in the system with the CTS and Afterrun sensor removal, but couldn't get the bleeder screw out. I ordered another screw and I'll use a screw extractor to get it out. I just didn't want to destroy it to the point that I couldn't get it back in.