w123 Outside Air Cabin Filter addition - PeachParts Mercedes-Benz Forum

DeliveryValve · #1 07-12-2014, 02:53 AM

I've meaning to do this project ever since I pulled my HVAC box, took it apart and found 30 years of nasty.

Just astounded we were possibly breathing this crap!

Evaporator

HVAC box Outside Air Inlet

HVAC box Outside Air Duct

Heater Core

To prevent this from happening again, is to add in cabin filters to the system. I will eventually get around to having both inside air and outside air cabin filters. But for this thread, the focus is on the outside fresh air side.

I had several thoughts on how to go about doing this including this..
Everyone rebuilding their A/C system should clean out their HVAC assembly box!

Cutting a slot into the firewall for easy access to the cabin filter was another idea. I agonized over this thought because I really didn't want to cut any holes, but in the end, it was the best choice.
My choice of filter is the readily available 2004-2014 Ford Mustang cabin filter. It's measurements are 7 inches x 8 inches. I thought it will fit fine with the narrow, mostly 7 inch depth cowling.

Here is the area I will be working on. Eight inches across for the filter is what is needed.

Inside the narrow cowling with the center outer cover, windshield wiper motor and arms removed.

Taped an outline for the new slot.

Oh my! What have I done!
The cutting has begun, no turning back now!?!!

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DeliveryValve · #2 07-12-2014, 02:54 AM

Rough opening.

Cabin Filter test fitted through the new slot. The left corner of the cabin filter hangs out of the firewall. A new molded door will cover the filter on the finished product.

Shot of the cabin filter through the cowling vents.

Shot of the cabin filter into the cowling. Looks pretty good to me so far.

The next step is to fabricate the filter base, filter duct and a firewall cover. Not sure which material I will be using for the base and duct. It might be fiberglass or sheet metal. Overall I think I am satisfied with the fit and will continue on this path. I will make updates to the thread when I make progress.

JB3 · #3 07-12-2014, 07:37 AM

extremely interested to see you progress!

DeliveryValve · #4 07-13-2014, 12:07 PM

Quote:

Originally Posted by JB3

extremely interested to see you progress!

Here is a bit more progress...

The issue with the w123 is the windshield wiper motor is in the way of the inlet to the HVAC box. The windshield wiper motor hovers over about 25% of the inlet hole, so placement of the filter directly above the inlet is impossible if you are keeping the original wiper motor. The final filter position is placed offset, and leads to a flow issue.

With the new duct narrowing on the right side of the inlet under the wiper motor, it will loose air volume. So to gain volume back, the left side has to be free flowing.

To do this, I have to remove the left cowling water dam. The new duct will be the new water dam, but the dam will be moved over a few inches because the filter is wider.

Here are pics with more gut wrenching surgery...

Drilled out the spot welds and wrangled the water dam out of the cowling.

A bit more breathing room under the filter now.

Tmadia · #5 07-12-2014, 11:42 AM

Cool project! Should be a really nice addition to the HVAC system.

DeliveryValve · #6 07-13-2014, 12:09 PM

Quote:

Originally Posted by Tmadia

Cool project! Should be a really nice addition to the HVAC system.

Thanks! I really want me, my family and any passengers to breath clean air in this car!

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ROLLGUY · #7 07-13-2014, 05:22 PM

I am following this as well. You might think about making patterns for all the metal pieces you will make, and offer them for a small fee so others don't have to "reinvent the wheel" as it were......Rich

bricktron · #8 07-14-2014, 09:55 PM

i turned on the fan abruptly this afternoon and blew dust and junk all over my girlfriend. godspeed to you.

DeliveryValve · #9 07-15-2014, 03:38 PM

Quote:

Originally Posted by ROLLGUY

I am following this as well. You might think about making patterns for all the metal pieces you will make, and offer them for a small fee so others don't have to "reinvent the wheel" as it were......Rich

Thanks for the suggestion. But I am not sure how much of a standard pattern I can create, it seems there will be a lot of contours that may not be conveyed into pattern. We'll see when I get to that juncture.

Quote:

Originally Posted by bricktron

i turned on the fan abruptly this afternoon and blew dust and junk all over my girlfriend. godspeed to you.

Thanks!

DeliveryValve · #10 07-23-2014, 04:01 PM

I decided I will be using sheet metal to fabricate the filter frame, duct and firewall cover.

I am using 22 gauge sheet metal. I think it will be sturdy enough to prevent any resonance and thin enough to easily manipulate.

For this round, I focused on the filter frame. Fabricated a channel piece and then made a basic frame.

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DeliveryValve · #11 07-23-2014, 04:01 PM

Test fitted into the cowling.

Next I'll have to figure out how to deal with the firewall slot surround because of the unevenness and fabricate the ducting.

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funola · #12 07-23-2014, 04:23 PM

Nice work! A lot of work also! As an alternative, is it possible to use RTV and glue a foam filter sheet (cut to size) that you can get from HVAC or vacuum cleaner filters to this opening?
Or build a frame that you glue into the opening and insert a foam filter?

Shawnb · #13 12-26-2016, 10:27 PM

How has this been working out?

vwnate1 · #14 07-12-2018, 09:42 AM

Three years later, did this work out O.K. or what ? .

DeliveryValve · #15 07-14-2018, 02:32 AM

Quote:

Originally Posted by Shawnb

How has this been working out?

Sorry it took so long to answer. Just never came back to this thread....

Quote:

Originally Posted by vwnate1

Three years later, did this work out O.K. or what ? .

I am definitely glad I installed this filter. I opened up the cowling earlier in the year when I had wiper motor issues during the rain. I wished now I took pictures, but that cowling was full of dust, dirt, twigs and little seeds. I just can't imagine not having a filter there to keep that stuff from getting stuck in the evaporator and not to mention breathing it all in.

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