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With the coming of heating season, i have been using my heater quite a bit.

On the one hand, I am happily remembering how good the heater is especially as compared to my BMW.

On the other, I am now getting bathed in black foam bits. That was common before. New this year, however, is CHUNKS of black foam. They sometimes come through the vents, but more commonly, they are strained from the airflow by the vent grills.
The driver's side dash vent seems to be the worst.

I spend several minutes with a little hook and needle nose pliers. I retrieved much of the foam blocking the vent. At least the hissing has stopped.

So - is there a brilliant solution to this problem? The foam must be coming from somewhere and now there is a fair amount coming out.

Is there a suggested way to remove the foam from the vents? Fishing it out works, but is a nuisance.

When will this stop? I want to wear white shirts again.

Edited 1 time(s). Last edit at 11/27/2019 09:22AM by JMstamford,ct. (view changes)
The infamous black foam comes from the air dams in the HVAC system.
After 10 or so years, due to heat, humidity and bad sourcing, the foam in the dams stats to deteriorate and just crumbles.
There are various solutions:
1.- Replace the complete HVAC unit at exten$ive co$t.
2.- DIY fix to repair the air dam foam. Not easy, not quick. Most give up.
3.- Don't wear white winking smiley
After some months, it will go away, although there won't be much control over the air diverting.
To accelerate the cleanup, close all air vents but one. Use a towel to close off the windshield vents.
Put a vacuum cleaner hose right onto the one open vent and turn on the fan full blast.
Use pick to help clear vent. Once that vent is cleaned, close it and open the next vent. Repeat until all vents are clean.
You may have to repeat the above procedure several times before all is cleared.
Happy Boxstering,

Pedro Bonilla
1998 Boxster 986 - 299,000+ miles: [www.PedrosGarage.com]

PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

If you live in a place where you drive the car in colder weather, you need a functioning heater. I had experienced the black/grey foam storms, and the lack of real heat. Like Pedro says, the issue comes from the mixer door that is meant to control the blend of heated and unheated air. The door itself has large holes - for reasons not entirely clear to me - that are covered by the offending foam. Time and heat cause the glue and foam to deteriorate, and the foam to exit the vents. The heated vs. unheated air can't be separated, so you end up not only with the messy foam problem but a lack of real heated air (it'll be lukewarm, at best).

There are two DIY approaches - one involves going in through the heater from the top (under the front cowl), and the other involves accessing the mixer door through the inside center vents. I performed the former (I don't think anyone had come up with the latter approach by the time I addressed the issue four years ago). As Pedro says, it was not easy and not quick - but I was able to do it and I am not the world's foremost DIY'er. Most of the work is just removing things to get at the mixer door (an argument for why the latter approach may be easier, but it does involve some cutting, IIRC). From there, it's just a matter of buying some 3M insulating foam at your local Home Depot or hardware store, re-foaming the door, and putting everything back together.

If you search "blowing foam" or similar on 986forum.com, you'll find a lot of good info and step by step write ups on it. Again, if you don't need good heat (maybe you put the car into 6 month hibernation - sounds like you're in CT) I'd just use the vacuum method. But you'd be surprised at how much foam keeps coming out. It's like you've struck the never ending mother load of great foam deep in the heart of the Boxster!


2003 Boxster Base - Midnight Blue Metallic, Savanna Beige, Metropol Blue
Pedro Bonilla
1998 Boxster 986 - 299,000+ miles: [www.PedrosGarage.com]

PCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)

Racecar spelled backwards is Racecar

"Racing is life. Anything before or after is just waiting" ... Steve McQueen as Michael Delaney in "LeMans"

"If you wait, all that happens is that you get older"... Mario Andretti

"Being second is to be the first of the ones who lose" ... Ayrton Senna

And what a questionable design in the first place.

There must have been a reason for the holes in the flap. Please tell me it was not to save weight.

Edited 1 time(s). Last edit at 12/02/2019 11:25AM by JMstamford,ct. (view changes)
but it seems to be a common design on lots of different cars so there is probably a reason, not necessarily a good one.
Some thoughts on blend door design

The use of foam is related to weight and price. Foam is much less expensive and lighter than the older approach of using felt. The foam (like the older felt) provides a few functions.
1) It seals the door way when its closed
2) It helps with NVH (reducing door noise as it opens and closes)
3) contributes to the weight and cost of the vehicle
4) The foam insulates, providing temperature transfer through the door

Those holes you see in the blend door frame material are there to allow the adhesive backing on the foam to stick together one side to the other, causing a much better bond than adhering to a solid metal frame. Think of the blend door metal component as a frame not a door. The frame is made of metal because it expands and contracts to temperature much less than the plastic the housing is made out of.

Anything related to the blend door is subject to the extremes of heat, cold, and moisture from both external air as well as the HVAC coils.

To work well the blend door must seal when close, and the material used must have high resistance to airflow through the material and low resistance to airflow over the material.

Now one can understand the reasoning behind the design and can make adequate determination as to what replacement materials would be adequate for repair.

Consideration needs to be given to using an adhesive and material that will last the life of the vehicle. I suggest considering dryer felt adhesive as it is designed to hold up to the extremes of hot and cold. If one lives in climates where the temperatures are extremely cold, then a silicon adhesive might be the better choice. Make sure the adhesive will perform at the lowest temperature as well as radiator temperature (about 200 F or 100 C). Of course the best adhesion is a mechanical attachment, just remember there are laws in play related to the physical operation of the door VS weight of the door assembly.

We know that foam is not the best choice to achieve the purpose of the blend door. Therefore it would be better to choose a thin felt which wool felt being the number one choice. Wool felt will resist moisture and perform well as a seal in both cold and hot conditions.

The best material would be a rubber seal that is affixed to the metal blend door by fasteners, the rubber seal would fit around the outer edge of the blend door. With the seal in place thin felting could be shaped and glued to the remaining door frame, thereby resisting flow through, temperature transfer through and allowing flow past the material.
Boxsterra - 2 years ago
The flap he fixes around 9:00 looks exactly like the Boxster heater flap. And because there's still foam when he takes it out, you can see how much the foam needs to stick out past the edge of the metal part of the flap. Great find.
I think this is the preferred way. The only invasive thing is the dremel of the top cap. Assuming that can be re-capped, and further assuming you can reach the third interior door, this repair should be the best choice.

Read the whole thread, the fix with better pictures was posted just weeks ago ...


The problem is that there are THREE doors that need to be recovered. (Two on one pivot)
See photo of the heater box exploded.


scroll down this thread for a picture of the pink servo and the pivot arm that must be removed to get out the bottom pivot point.


reviewed together, these threads seem to illustrate the best way to do this repair. To be clear, the "right" way requires removing the entire dash and there is NO WAY I am doing that. This method seems to be viable and mostly nondestructive.

Edited 1 time(s). Last edit at 12/16/2019 10:49PM by JMstamford,ct. (view changes)
Boxsterra - 2 years ago
The fix depends on what you're trying to achieve.

If you're looking to get rid of all foam bits or make sure air only comes out where you have set the HVAC system you have to take the whole system out, which requires removing the dash and a lot of labor.

If you're looking to just fix heating and A/C performance then it is much easier. I've seen two shortcuts doing this.

(Note that there are many possible causes of A/C not working - this just fixes one of them, namely A/C not getting cold enough because some heat is mixing in)

Method 1:
(more pics)
- (Under dash) disconnect heater flap servo and lower flap retainer cap
- Remove cowl and cover over heat exchanger
- Remove heat exchanger
- Dremel plastic on top of heater flap
- Pull heater flap out and cover it with tape/foam/whatever
- Reinstall

Method 2:
- Center console - pop out plastic bits on either side
- Unscrew center console and pull it towards you
- Cut heater duct and fold back so that you can see heater flap
- As much as possible with limited access, clean heater flap and cover with tape/foam/whatever
- Fold duct back in place and affix with tape/glue/whatever
- Put center console back in

Several people have reported success with both with not too much time spent. Not having done either, I'm on the fence as to which is better.
Boxsterra - 2 years ago
On the parts diagram there are 4 motors, which suggests 4 flaps (heat/AC mix, defroster, center vents, footwell vents). But as I said above, unless you're fixing air diversion or stopping the foam shower you only need to address one of them.

Parts # 6, 11, 14, 16
The fan comes out pretty easily and it looks like it would give access to any door directly above it. Of course, we cannot see the route of any ducting, but there does not appear to be much space there.

Indeed that might be the actuator for a flap determining re-circulation from fresh air. It almost looks like the cabin air filter would be just above the top opening depicted..

Edited 1 time(s). Last edit at 12/17/2019 02:33PM by JMstamford,ct. (view changes)
Good video
Boxsterra - 1 year ago
This guy just made a video where he goes in through the center console. You can clearly see the flaps and their operation. Definitely helpful.

This shows the orientation of the doors and what needs to get redone.

One of the video comments...

Edited 1 time(s). Last edit at 04/04/2020 11:07AM by Boxsterra. (view changes)
I replaced the foam by cleaning all of it off and then replacing it with thin but somewhat firm packing foam. I held it in place by using spray adhesive. As I wrote no a hard job to do and really didn't take a long time.
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