I have a 1999 4runner that's been a champ for me for years but apparently some rats (or maybe squirrels) hate my 4runner and decided to make a nest in the HVAC system while I was deployed. I pulled the fan out and found pretty much the same thing as in the picture in this thread - a rats nest. Cleaned it all out but now I'm looking for where they came in at and I'm thinking maybe through wherever the fresh air comes in when you have "external" air selected. Anyone know where that is?

 

I believe it is the plastic grill below the wipers, I believe small animals can access this area from the fenders and hood attachment points aswell, best bet is to switch the fresh air to recalculate, theoretically this should close off the access into the cab/HVAC.