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I experienced a loud rattling noise when I turned on my Mazda 3's A/C for the first time this season. So, I decided to take apart my ventilation system (cabin air filter compartment, and intake duct under my windshield cowl).

It would appear that someone made a nest in the intake duct, right up against the intake flap/damper:

Mouse nest in cabin air intake duct

The nest is mainly composed of chewed-off bits of the fiberglass heat shield from my engine compartment. My working theory is that they packed so much material in there that it forced the flap/damper open, and material was pushed down into the ductwork where it lodged against the cabin air filter. Of course this brought moisture into the vents as well and effectively ruined the filter.

Since the Mazda cabin filters are notoriously difficult to access, I'd like to prevent this from happening in the future. As you can see from the photo, the holes in the grate over the intake duct are quite large, easily enough for a mouse to slip in through.

My thinking was that I could try to fit some sort of mesh over that grate - but what kind of mesh would:

  1. be fine enough to exclude mice;
  2. be strong enough that a mouse couldn't simply push it aside or chew through it;
  3. allow enough air flow without putting excessive strain on the blower motor?

Is it possible that there was actually another filter of some sort that has gone missing?

  • There may be simpler method ... I understand just an average household fabric softener sheet will keep the rodents away. I understand it works, but I don't know this for sure. – Pᴀᴜʟsᴛᴇʀ2 May 22 '17 at 1:24
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I was going to suggest something like body filler wire gauze but if I remember correctly rodents chew through that. We had mice in a caravan once that chewed through body filler gauze rather easily.

So I'd suggest chicken wire.. I know its got quite large holes in it, but if you buy say a metre or two of it then fold it over itself many times this will effectively make the hole spaces smaller each time you fold it.

  • So I guess my concern is - would this place undue strain on my blower motor? – alexw May 22 '17 at 16:12
  • No, not at all.. The only way you'd put an excess load on the fan motor would be if you virtually cloggeg up the space in your picture.. A few folds of chicken wire with say 10mm holes would be fine. – Orb May 22 '17 at 16:17
  • Thanks! I actually have some extra chicken wire laying around - I'll try it! – alexw May 22 '17 at 17:11

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