The center vent comb flap provides a restriction to the airflow through the center vent when floor or defrost flow poaitions are selected. The default/fail condition is comb flap closed. There's some function to the divereter in the front manual flap than helps with heat/cool blending, but that's totally separate.

On your door/center vent flow question, they have flow output available all the time when any output selection is made on the slider. Your temp slider position is compared with inside and outside temps to decide how much heater air to mix via the blend door motor position, and whether to allow coolant flow through the heater core for added heat. The temp control is separate from the outlet vent control.

If you ned to continue this discussion, go ahead and start a new thread with the new subject.

 

Dr bob, Thanks for your input. Before I start a new thread I will search the forum for further details to better understanding how the system works. I would hate to waste everyone’s time with a question that has been discussed.

 

Don't be afraid to ask or post a question. My suggestion for starting a new thread was to make sure that your different subject gets a thread of its own, making future searches by others more meaningful.

I'll be the first to suggest that there's only a handful of folks who truly understand the thinking that inspired the HVAC controls. They are probably still drunk, living under AutoBahn overpasses just south of te factory. The rest of us have to muck our way through it all when something goes wrong.

 

In a follow up for this, I took the centre consol out so i could troubleshoot the centre comb. What I found was that the centre comb was actually stuck very firmly behind a seam that seems to be directly under it in the airbox. As a result of this the plastic bit that joins the comb to the actuating arm has actually snapped off. I have trimmed the seam and the bottom of the comb with a dremel so at least it now moved freely and with the fan on it lifts up and I now get more air through the centre vent, which was always weak before. I have not figured out how to fix the broken part. If the airbox was out of the car that would be easy but I really don't want to take the dash out. I'll wait for some more inspiration.

 

[QUOTE=dr bob

I'll be the first to suggest that there's only a handful of folks who truly understand the thinking that inspired the HVAC controls. They are probably still drunk, living under AutoBahn overpasses just south of te factory. The rest of us have to muck our way through it all when something goes wrong. [/QUOTE]

Ha-Haaaaaaaaaaa, almost dropped my Hobnob.... English cookie.

I'm in the middle of sorting my my HVAC too.

 

There are a couple of things that do not make any sense to me about the HVAC system.

1. The comb flap? why just partially restrict airflow when you can do that with the vent flap? seems redundant to me.

2. Why in the world did they set up the recirculate flap to only be open when the system is off, ie the black square position?
It should have been a independent control.

Over all I think it is a good system, for what it is.
I hope I never have to get into mine again, but time will tell.

 

I'll let you know how i get on when I can be bothered going in there again, but it annoys me that its not working the way it should. My current plan is to replace the connecting arm with a steel piece that screws on to the comb. I have already dremeled out the rivets that hold the comb to the hinge/mount and replaced the rivets with screws but i did not ahve any suitable steel to hand to put on and was not too sure about the geometry needed as the connection does not seem to simply protrude in a straight line.

By the way, the hinge is not really a hinge as far as I can tell just a piece of thin plastic that bends. What with that and the obvous flaw in the form of the seam that snags the comb (and results in either that clack clack sound or a broken pivot) and the lack of access to get to the arm connection has to make this one of the poorest thought out bits of the system.

 

I GAVE UP... PLUGGED THE ACTUATOR LINE FOR CENTER ACTUATOR AND CAP THE MALE END...MANUAL CONTROL THE VENT DIRECTION...ICE COLD AC-NO MORE CLACKINGGGGG..

 

By the way, the hinge is not really a hinge as far as I can tell just a piece of thin plastic that bends. What with that and the obvous flaw in the form of the seam that snags the comb (and results in either that clack clack sound or a broken pivot) and the lack of access to get to the arm connection has to make this one of the poorest thought out bits of the system.[/QUOTE]

This comb flap hinge has my attention at the moment. Does anyone have a picture detailing what this hinge looks like? Mine broke when replacing the vacuum diaphram and seems to work quite well when I duct taped it back together. Has anyone come up with a fix without removing entire unit? I would prefer something like a leather strip glued to resemble this hinge for the time being.

Thomas

 

I've got pics of it.. see this thread:

https://rennlist.com/forums/928-foru...uator-arm.html

I have higher res ones of those too.

 

Hilton,

Thank you for all this documented info you provide on this repair. A great job with the pictures also.
I see where the comb flap is broken on yours, mine is broken where it hinges to the piece that is riveted to the top of box. From what I understand is that it might be connected in two spots. I am trying to understand if this comb flap snaps into the upper support piece that it hangs from or is one complete piece.
Thanks again.
Thomas

 

Some extra pictures, just in case. I had quite a fun time to reconnect this when I replaced the diaphragm, so can understand the need for inspiration to fix it....

 

This pic might help:

The comb is riveted with 3 rivets onto the hinge. The hinge has 2 joins, and is indeed a bendy bit of plastic. Then there are two rivets which join the base of the hinge to the airbox.

I removed my hinge from the airbox to effect the repair - this shot is after the repair was made (hence the small aluminium bracket on the right side - this is a RHD car, but the exact same hinge part is used in LHD and RHD - hence the other attachment point on the left side of the picture used in LHD cars). WHen I riveted the hinge back to the airbox, I used a couple of small washers around the heads of the rivet to spread the load, so I didn't just crack or pull through the plastic.

 

Hilton,
This is a great picture of where my problem is. The thin plastic hinge on each side is broken or it has come apart. Do you recall if these clip together or are one piece which would make this one complete part number(flap and top mount)

Thomas

 

The hinge only has a BEHR part number on it - 90 412 06 007

The comb itself has both Behr and Porsche part numbers - so I suspect the comb and hinge are supplied as a single unit to Porsche.

Porsche part number for the comb flap is 928 573 505 04 - although like other sub-components, it may not be possible to buy separately?

As far as repairing it goes - leather would work well IMO. Another possible alternative would be Kevlar tape from a sailing store - although it may not be supple enough.

You could probably effect a temporary repair using cloth tape (aka "Racing tape" in a lot of automotive shops) by lifting the comb flap up and reaching in through the dash vent?