My wife noticed something peculiar with her '01 S8 and I am not sure what is normal. We have only had the car for a couple weeks.

The AC air does not come out of the drivers side lower dash vent (the one next to the door), or the rear outlet in the B pillar for a few minutes after the car is started. The passenger side equivilants seem to work from the start. This doesnt seem like normal operation but I want to be sure before I bug the dealer.

I ran some of the output diagnostics on the HVAC with my VAG-COM tool but no DTC were reported. I am not sure what all is tested with those and if this is specifically covered.

 

I know when I start mine in cold weather, she won't turn on the fans untill she can pump out the hot air I am asking for. If left/right controls are set differently - this may have summit to do with it.

 

I had a problem with my HVAC system when I first got the car, it wouldn't blow out cold air (or really any for that matter) unless the temperature was set really low. Then it would work like a champ.

It ended up being a motor that drives the fresh air vent, the potentiometer that is associated with it was gone and it couldn't provide proper feedback. So the fresh air vent stayed closed when it should of been throttled open, therefore, the fan was taking suction on a closed vent, therefore no cold air until the temp was really low, then it could open the vent and suck fresh air to feed the cabin.

In order to test it using the VAG-COM, you need to run it through a calibration test before it will pick up codes. It drives all the vents and motors through a cycle to pick up high and low voltages/resistance. It looks at the high/lows and sees if there is a problem. As I recall, it didn't have a code until I ran the test. I can't remember what channel it was, but if you have the tool, you probably know how to use it.

I changed the motor, and recalibrated the system and it's worked perfectly ever since.

One additional troubleshooting method to determine if it's the fresh air intake vent is to start the car on a hot day and put the A/C in the recirc mode right away, it takes that damper out of the circuit. If you get air blowing right away, you know you have a problem.

However, this doesn't sound like your problem.

FYI, my car won't blow out those vents for about 10-15 seconds after start up on a hot day, you can hear the vents realigning then it comes out.

pw

 

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if I raise either the driver or passenger side temperature setting, I can hear the fan on that side reduce speed and eventually shut off. The result is as you describe -- no air from the lower dash vent and the B pillar outlet on one side only. With both the driver and passenger side set at the same temperature setting, I get equal flow to both sides.

Next time I'm on the track, I'll take advantage of this little feature to try to keep the motor temperature under control. At Mid-Ohio last week, the water temperature gauge was running just one tick mark below maximum.

1. Turn econ "on" to turn A/C "off" [I always do this.]
2. Set driver side temp to "Hi", turning driver's side fan off
3. Set passenger side temp to 60 oF, turning the fan on that side to max

My sympathy to the instructor who always rides along for the first session, but maybe this will insure that I immediately get signed off to "solo" :-)

 

What I observed yesterday was the vent had no output for a couple minutes, then worked.

It seems today to start flowing immediately. Maybe my cycling thru the diagnostics did something.

By the way, the climate settings were the same on the driver and passenger sides.

 

After thinking about it a little more, my description of what happened to my car would be similiar to yours, but for a different flapper motor. As I had mentioned, sometimes you will get an error between where the motor is told to position and actual position. It is when the register values of actual versus supplied is more than 5 units. If you have the Ross-Tech software, you can see what the computer is telling the system and what the system is reading (for something like the 15 channels of the HVAC system).

The range is usually from 20 or so to 120 if I remember correctly. That corresponds to full open or full close. As you change the temperature, you will see the target numbers change then the actual input from the device in the computer. It will move from 40 to 73 for example, and the actual will usually be within one of the target.

If you have a resistor or whatever they use for position indication of the flapper motor shaft going bad, it won't be able to mechanically move the flapper to its correct position. If the system doesn't respond within ten seconds max, something is probably wrong.

I played with my car this afternoon, put the driver's side temperature from 74 (both were on 74 in auto) up to 80. At first, hot air from the heater came out the side vent, then I felt it switch to both the side vent and the floor vent. So from this information, it appears that the vent should normally be open, especially in these months because you want the car to be cooled after sitting.

It sure sounds that there is a good possibility that the flapper motor that operates the damper that supplies air flow to the left side vents is going South. Not that hard to believe, probably marginal from the factory. Take the temperature to a low limit so the fan kicks on high and I bet it starts blowing hard through the side vents because you are at the limit of the signal, and the vent will open.

If it does that, than plug in your tool again, I bet there is a fault code. Make sure you don't erase them if you find one. Write it down, word for word before you erase it.

Paul

 

Another reason why I should stop postponing and buy the Ross-Tech software

 

Excellent suggestion...Thanks!