HVAC/Cabin Air Filter, Rodents, and... A Mystery

Greetings all. Most Taco owners on this forum are well aware that the HVAC fresh air intake of their truck is a great nesting place for rodents, right on top of the cabin air filter. If not, see these threads:

https://www.tacomaworld.com/threads/rust-varmit-and-ac-clogging-prevention-project.557970/

https://www.tacomaworld.com/threads/cabin-air-intake-screen-mod.566441/

These are just two of many threads on this subject. Thanks to *everyone* who has posted and shared pics and tips for doing this mod! I am waiting right now for a piece of the steel mesh gutter guard to arrive so I can complete this on my truck.

Now for the "mystery" part:

In at least one of the many threads on this, somebody made an excellent suggestion: Always set your HVAC settings to "recirculated" before turning off your truck [in re-circ mode, a door closes over the opening, sealing it quite well]. In the process of cleaning all the debris out on my 2014, I discovered that the door actually closes whenever the ignition is turned to "off," no matter how you have the fresh/re-circ button set...

So the mystery is how the heck are these evil little critters getting in there???

After a lot of head-scratching, I have two possible explanations, but both seem lame to me:

1. Maybe the door was blocked from closing completely by a random chunk of something. This sounds good until you consider that said random chunk would have to stay in place over time, to allow the apparent ongoing use of the nesting area. No obstruction was found on my truck; the door closes completely and seals tightly.

2. Maybe the door doesn't always close when the truck is shut down. Possibly some combination of HVAC settings and/or other variables could cause this? Need an expert on Taco HVAC systems to weigh in on this.

It seems like the only other explanation is that there is some other way for rodents to get in there... But then they would have access to the entire HVAC system [and possibly the entire truck interior]. If that were the case, then why would they always pick that same spot on top of the filter to nest? [Time and time again. If you search for threads on this, you will find a *lot*.]

Any and all suggestions, theories, random digressions, flamings, etc. are welcome. Thanks in advance!

-Jim

 

I believe the default position of the recirc door upon cutting off the ignition is open.

 

Hi, thanks for reading my post.

Yeah, I guess that is really the core question. On my 2014, it seems that the door closes when the ignition key is turned off, regardless of where the fresh/rec button is set. But the only real proof I have of this is observing it on a cold truck [overnight cold]. So for all I know, under some other shutdown conditions, it might not close.

For example [wild speculation here], maybe when you shut down the truck with a cold AC evap coil it leaves the door open. Or a hot heater core. Or some other reason.

The only other explanation is that there is some other way for mice to get in there.

Has anyone ever found a mouse nest on their cabin filter AFTER installing the wire mesh over the air inlet? Inquiring minds want to know... [That's a line only geezers like me will remember.]

-Jim

 

Yes I had mice in my truck after blocking off the cabin filter inlet. No idea how they got in.

 

Hmmm, interesting. Did they build a nest on top of the cabin air filter, by any chance?

Honestly, the more I think about this, the more it vexes me. A couple more points to consider [please bear with me here]:

1. On my truck, there was a nest on the top of the cabin filter, but NO evidence that the mice had gotten past that and had access to the rest of the interior.

2. In another thread, someone posted an image from a service manual showing a partial cutaway view of a Taco HVAC system, but I can't tell from looking at it what actually happens in there with all the doors, ducts, etc. The question here is, when the door is open, does it completely close off any possible rodent path between the inlet side of the filter and the interior air inlet? It *appears* that it does, at least on my truck [2014]. But I am not 100% sure.

It is a dilly of a pickle...

-Jim

 

They will also visit your engine air filter..........

 

Oh yeah, will they ever... who would have thought cute little furry critters could so be rotten to their filthy #!^$ing cores!

Seriously, rodents may well be the end of us when the next plague comes. I think we have gotten way too complacent as a society about them - exhibit "B" for this argument being the design of modern vehicles.

Exhibit "A" would be the way we construct our buildings, which is sloppy tbh. Half-assed MEP penetrations that leave plenty of entry points, building materials that become nesting materials, easy-to-chew plastic shit, etc...

But I digress ;^)

 

Mystery solved.

Got my piece of gutter guard today and went to cut and install it. Had to move the truck first, engine was running for about five minutes. Shut it down, and the door stayed open...

So the behavior I was seeing earlier [always closing] only happens on a fully cold engine. I have no idea why.

Sorry for wasting the time of anyone who read this far. I added a banana, so at least there's that...


Resume lurk mode...

 

Thank you, OP, for this thjread and the links to other TW threads you included. I had some sort of critter get into my air ducts and died last week. I had no idea where the entrance point was for outside air to get into the cab, and now I do. I will be working to fix this in the next couple days, thanks to you!!