Addition of a screen to the HVAC inlet

HVAC inlet grille

The cabin air filter is really just a screen to protect the fan from leaves, twigs, a mouse nest and other matter – and really has no filtering effect in reference to cabin air quality. And a screen at the cowl opening would hopefully keep a mouse from creating a nest in there.

What is labelled as a side cowl grille, is in reality, a bezel desperately in need of a metal screen mesh to keep critters, leaves, twigs, etc. from finding their way into the cabin air blower fan, unless you are quite confident that your car is kept in a clean, critter-free garage, when not being driven.  I doubt that the one integral strip of plastic serves as a beneficial barrier against anything other than perhaps your fingers.

Goaterguy was probably quite surprised to find a mouse nest in his, and added a metal mesh screen to prevent that from ever happening again (they chew through plastic, so don’t go through all the work of adding a screen made of plastic).  I know from experience in a camping trailer, that the urine smell never goes away, but hopefully his mice that spent the winter left the nest (and vehicle) for that activity.

HVAC inlet no-grille

photo courtesy of Goaterguy

And since the air-flow needs to be unrestricted, I would suggest also avoiding the installation of any “filter” meshes, like window screen,  as it will clog with dirt just like the air filters for your engine and furnace, and become another maintenance task (will need to be checked and cleaned periodically – not ideal).

In anticipation of taking on this project, I ordered a sample of gutter guard from ($2.75), but you could probably procure a 3′ panel for around $5 at your local hardware store.  Since my car is kept in a garage free of  critters (thanks to a tightly sealed garage door and an ultrasonic pest repeller, after lifting the edge of the passenger side cowl panel to see everything looking like a new car, I gave up proceeding with this project.  My understanding is that , in addition to the interior A-pillar and header panels, and the exterior windshield surround panels, the cowl grille panels too, need to be removed when replacing the windshield.

It is not easy removing these panels though* !!!

But for those that might wish to proceed (Steve Southwell advises avoiding putting much pressure on the lower overhanging edge of the windshield)…


1. Remove both wiper arm assemblies (note which is left and right and their orientation, so that you can later replicate their position on the splines).

2. Disconnect washer hose B from joint pipe A (twisting back and forth wile pulling).

3. Detach the weatherstrip clips A and B (what a PIA; actually it might be best to stretch the rubber to separate the clips from the weatherstrip, leaving them in place on the metal body).

cowl panels1

4. Remove the detached weatherstrip.

5. Remove the hole covers.

cowl panels2

6. Remove the (phillip head) screws.

cowl panels3

7. Pull the cowl grille in the direction of the arrows shown in the figure and detach the cowl grille hooks from the body.

cowl panels4

8. Pull the cowl grille in the direction of the arrows shown in the figure and remove the guides from the windshield.

cowl panels5

9. Detach windshield washer hose B from the cowl grille hook.

cowl panels6

10. Move the cowl grille (RH) in the direction of the arrow shown in the figure.

cowl panels7

11. Move the cowl grille (LH) in the direction of arrow (1) shown in the figure.

cowl panels8

12. Remove both cowl grilles (LH and RH) in the direction of arrows (2) as a single unit.

13. Remove the side cowl grille carefully so that you can reuse the foam gasket.

14. Trim the screen mesh to fit on the underside of the grille, and fasten with hot-melt glue and a couple of small tie-straps.

hvac screen

Heater intake 3

nice job!      photos courtesy of napastar

15. Reinstall everything in the reverse order of removal.

12 thoughts on “Addition of a screen to the HVAC inlet

  1. I added a screen when I had to take the cowl off to install a strut tower brace. My word of caution from experience is to avoid putting any pressure on the lower windshield lip under the cowl. I leaned my palm on the bottom near the corner and the windshield cracked. Fortunately I had added $0 comprehensive so I was covered.

    Liked by 1 person

    • I can only guess that an unusual pressure point like a flash weld must have been in just the “wrong” spot. Or perhaps Mazda has programmed the robots to skimp (gram strategy) on the butyl rubber application. Did the installer of the replacement windshield notice anything requiring attention along that bottom edge?


      • The windshield glass has about an inch and a half of unsupported overhang on the bottom edge. This is the portion I leaned on. Enough of a fulcrum to cause the glass to fracture. I think the OEM glass is of an eggshell quality.


  2. Great write up, all instructions in one place. Only needs to be done once to prevent debris from entering or critters nesting. Allot easier do do this than cleaning up the aftermath of the critter.

    I had to also remove my blower and sanitize it and sprayed a bunch of Lysol into the intake to sanitize that amd the whole system. Stink is gone.

    Liked by 1 person

  3. The issue seems to at least go back to the NC Miata so I don’t understand Mazda for not doing anything against it. There is a range of threads about it on the Miata Board.

    Ordered a sheet of Stainless Steel wire mesh from The Great River ( ) and had it installed during my last service in April.
    Dealer did it for free, since they had to keep my car a day longer because they couldn’t get the smog test done in time due to the whole COVID situation.

    Liked by 1 person

  4. I wish the access looked easier but adding the screen is a good idea. Years ago I bought a 20-year old F-250 truck that had been parked out under trees for years. Days later the cab filled with smoke that smelled like a wood fire. Turned out that dead leaves and twigs had gotten all the way into the resistor pack that controlled the heater fan speed and had ignited when I set the fan on low. (My Classica lives in a garage!)

    Liked by 1 person

    • Hi John,
      luckily this isn’t a concern with the 124/Miata. Mazda placed a plastic wire mesh just before the blower motor. Leaves and dirt accumulate there so you have to only worry about it getting blocked and limiting airflow. Don’t know how this is handled overseas but here in Germany it’s changed during every other service. At least that’s what the service protocols say and what the dealer charges me for 😉
      However it’s a job you can do yourself, although you have to remove some interior panels and unplug some cables. It’s a more tedious task than it has to be though…
      Also I’d recommend removing the blower motor first (which for some reason is way easier than removing its “filter” o0) before pulling out the mesh. Had it happen to me that leaves slipped off it and fell right into the motor.


      • Tobias, if you are talking about the cabin filter, that is AFTER the blower motor, on the outlet circuit. I’m talking about the inlet port, or have I misunderstood?


      • Hi Dan,
        I think we are indeed misunderstanding each other ^^

        I was talking about the plastic mesh insert above of the blower motor.

        I’d say that this is very much before the blower airflow-wise. Else there wouldn’t have been any leaves, dirt etc. for me the remove 🙂

        Pulling the filter insert will result in some of the dirt accumulating in it to fall down into the blower motor if you haven’t unbolted it before. Not saying that this happened to me 😉


      • OK. Wow, that looks like what is called the cabin filter, but apparently I’m not positioning it properly in my imaginary HVAC system layout.

        I thought the “gerbil wheel” visible under the screen here was the the blower fan 😉 [added 8/19/2020], but I now believe that is the heat sink for the blower motor resistor instead (for low and medium speeds).


  5. I just installed a shock tower and while I had the cowl off I ran into the same issue. Loads of garbage in the air intake, did a little vacuuming & it was definitely worth it. The grill inside was totally covered in crap & now I noticed a substantial increase in air conditioning air flow that just wasn’t there before. Like the idea with the screen on top, my next mission. Off to Lowe’s for screen
    Thanks for the idea, really appreciate it 👍👍👍
    Tom Nagle – 2018 Fiat Spider

    Liked by 1 person

  6. Pingback: Differentiating Cabin Air Issues With Your Nose | 21ˢᵗ Century Fiat / Abarth 124 Spider

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