oldAGE

Hey folks -
Stupid question of the week from AGE:

I place my Four-Zone Climate control in Auto. Place it in Sync. Set my temp. All is great. Notice that the A/C light is lit. It's winter in WI and I really don't have fogging and defrosting issues especially when the air is cold and dry. On all four of my vehicles with electronic climate control, I normally switch the A/C off and let all the other Auto functions do their thing.

I know that on my Subaru's, they look at the Outside air temp and force on the A/C for start-up defrosting. My Murano says "I can do that too but if you turn of the A/C, that's what you want so I'll just leave it as you set it..."

On Audrey (my A6), I have the Auto and Sync on, the A/C off... and it stays as set at start up. When I check my Efficiency Program, the A/C is always indicated as consuming energy. Today, it's 53 degrees and sunny so my black interior has gotten really warm and I can feel the change the Auto function made to setting the airflow to the dash vents to help cool the car down. Again, the A/C shows in the Efficiency Program. Of course, I don't know if it's drawing cool (53 degree) outside air or A/C air.

Anyway - what do we know? If I set Auto on but turn A/C off, does Audrey just "flip me the bird" and says, "I know what's good for you so I am ignoring you and the A/C in Auto will always be on!" (sort of like Microsoft) -- or am I missing something.

It seems that the manual is of no help regarding this matter. I think I read everything there that needs to be read.

Thanks.
AGE

snagitseven

Auto means just that. In winter the system will work the A/C for dehumidifying, heater, vents and fans as needed to maintain a comfortable environment based on your temp setting. Turning off the A/C would defeat this goal. Keep in mind the compressor in winter is not activated full time so the fuel consumption difference is pretty nominal. I set my temp to 68 degrees on auto and have never had the need to change anything else since the car was new almost 5 years ago. We are always comfortable.

newmoon

Agree with snagitseven. It's actually a variable displacement A/C compressor, so when it's cold it reduces its output and also uses very little engine power.

This is also the reason why you should NOT crank it to LO when it's hot because then the A/C compressor runs at max output and wastes power. Just set it to your desired temp and let it do its thing.

oldAGE

Thanks for all the input. It is appreciated.

So here is my logic. While I accept the fact "that's how it works," I reject the design premise and here is why:

If my interior heats up while sitting in the sun on a 50 degree day, and I set my Auto to 72 (while snagitseven likes 68, I am a fan of 72), the temperature inside the car could very well be in the 80s. Assuming I keep the sunroof closed and the windows up, the Auto is saying, "Hey, you like 72, it's 80 in here, I need to cool down. So I am going to change the vent positions to Dashboard (from footwell for heat) and I am going to cool down the interior by running my A/C."

Well, it's 50 degrees outside and there is no way, no how, that any compressor based cooling system is going to drive temperature as low as 50 degrees. So why not say, "Hey, it's 50 degrees outside so I am going to vent the interior air out the back (which it actually does) and draw in that nice cool fresh 50 degree air from outside and I'll just keep my compressor off."

Sure, it actually may work that way as newmoon alludes. And as snagitseven writes, it's there for humidity control. And as we can all assume, it's not really consuming too much energy nor is it affecting performance in this highly tuned engine... But....

And thanks for the input. The more I know, the better I feel.

AGE

gk1

I think it is more a poor terminology thing.
The efficiency status in the DIS display is simply telling you HVAC is "on" and should be making no distinction between A/C actually on or off. If you shut everything off completely (no fan) you should see the line disappear. I know it says A/C in the display but i think it is just poor terminology on behalf of the efficiency display.
This could be confirmed with VCDS logs as I believe it tells you if the compressor is actually on or off.

newmoon

If you have time, you can read the Self-Study Program from VW/Audi on air conditioning:
www.volkspage.net/technik/ssp/ssp/SSP_208_d1.pdf
www.volkspage.net/technik/ssp/ssp/SSP_208_d2.pdf

It's not just about temp e.g. 50F outside so use that air instead of A/C. The A/C is always used to dehumidify it as well. Plus blowing 50F air at you wouldn't be comfortable so the system also heats it back up to say 70F. This is like how the weather report gives you a "feels like" temp which takes into account humidity and wind chill.

There are curves used that give the best air temp and flow depending on the ambient temp like this one from the SSP:

oldAGE

Cool. I like to read.

As far as 50 degrees blowing in one's face... yeah, I would suspect a bit of fuzzy logic intelligence in the system mixing air Temps to gradually get it to the set temperature. I can understand the humidity issue too. And the more bodies in the car and the wetter the boots are etc. I guess at the $58K level, one should not care.

Thanks for the info.
AGE

snagitseven

I would add the system is smart enough to determine when to turn off the outside air circ. i.e. polluted air.

Finally, if you're unhappy about the way the automatic climate control is designed, just turn it off and operate the fans, vents and circulation as desired.

FwyFlyer

That's what I was looking for. How do you turn it off?
TIA

DanfZX14

Push the auto button, the red LED on the button will go out, then you can manually make adjustments.