928 at last

Hi All,

I should know the answer to this, but....
Is there any position of the lower slider that will result in there being no or very little airflow through the centre console vents?
Seems (Even after a re & re of the vacuum system) I've got a fairly high volume through the centre vents at all settings...?
TIA!

Randy V

While driving or sitting still?

928 at last

Both actually.

davek9

What year, or did I miss that?

928 at last

You missed it. 1990 S4

Alan

No - on a '90 (and most years) there is no automatic flow control for the center vents. You will get less flow in defroster (up arrow) or footwell (down arrow) and less still in Bi-level (up & down arrows) modes - but only because additional outlets opening reduce the flow rate.

You must use the manual vent control to reduce flow further.

Depending on temperature settings the comb flap operates to ensure a heater core bypass and this can slightly change the airflow rate - but its purpose is mainly to reduce AC temps for max AC cases.

1980-1983 models did have a dual level automatic control over the console flap flow - in a way they were the most advanced systems wrt airflow control. This was removed in 1984 and became manual again.

Alan

928 at last

Thanks Alan!
That's what I needed to know.

The Forgotten On

I have an 81 and there is a flap with some holes in it that reduce flow behind the pneumatic center console flap. It is where the comb flap is on later boxes and it can reduce air flow quiet a lot actually.

The combs, as explained above, don't really affect air flow too much. Good luck on seeing if there is an issue or if it was the way the HVAC in your car was designed.

Alan

After '80-'83 the pneumatic center console flap itself became extinct... so most folks won't even know what you mean... by '90 it was a distant memory.

It sounds here based on what we have been told that everything is working as intended.

Alan

928 at last

I believe Alan is correct based on the amount of work and effort that went into the Re & Re, and the parts deployed. I was actually expecting the system to respond with a serious decrease in centre console airflow when other options were selected....that's what threw me off.

Alan

The center console vent is basically the shortest airflow path - so it will always tend to have the highest airflow of all the open vents. If you want to change that you need to use the manual control. In cases like defrosting - you would do best to close the center vent (and door vents) to maximize flow - select defroster vents, max hot and full fan - don't use DEF for this (the addition of AC doesn't help defrosting speed one bit).

For emergency defogging select DEF and close console & door vents; the maximum airflow, max heat and dehumidification by the AC clears the screen the fastest. In the 80-83 cars you get this by default in DEF - which is great for safety.

When you hit freak conditions that can cause rapid windshield fogging at speed - you quickly realize how critical this feature can be...

Alan

dr bob

In my deep dark past, I bought a used Saab Turbo for DD duty, and it came with a gaggle of design documentation. Most was detailing the "why" on what appeared to be odd "features". Ignition lock on the bottom of the center console by the base of the shifter, so the wad of 'other' keys wouldn't tear up your knees in an accident. One discussion was about the airflow through the center vent. Similar to the 928, the center vent offers some cool outside fresh-air flow when you have the heater and/or defroster in service. So you can stay awake with all that warm air flowing around. In my later 928, you can bias the flow with the center vent lever, but in general if you aim the top grill towards the driver for cool air, the bottom vent towardsthe passenger with warm air, you have it per design. If you want just warm air both upper and lower, move the little slider to half-way or so, and reduce the amount of unheated outside air.