Air blowing out of rockerpanels

I just replaced an o2 sensor on my 96 Tacoma. I started the engine and crawled under to check for leaks and was surprised when air blew in my face from small holes at the bottom of the rocker panel. I found it coming from both sides and only when the heater fan is on. My truck is an extra cab so I thought this was ventilation for the back seat, but no air blows out inside the cab back there. Why does Toyota put air through the rockers?

 

it does not happen with the air running?

 

It comes out of the holes anytime the fan is on and it is switched to outside air.

 

When on outside air, the cab is pressureised; the air vents out the cab back or in door vents (I can't remember where the vents are on 1st gens),but the vents don't have much surface area, so air still leaks out of the door handles, weather strips, anywhere it can, so some probably just leaks through the heater to firewall area, and some will always blow out the drain tube. Try putting system on outside air and open drivers window 2-3"; this will let most of the volume out, and only just a very little should vent out the rocker panels, if quite a bit still exits out the rockers; I would look for a damaged foam gasket where components bolt up to the firewall, either inside or outside the vehicle.

 

Hi. I was on vacation for the last week and wasn't near my truck. Opening the windows does stop the air from blowing out. I never realized the cab was that pressurized. I also never knew that the rockers were open to the inside of the cab. I guess this will keep the inside of the rockers dry, Which may help prevent rust. Living in Pennsylvania that could be a plus. Thanks for all the help. Gary