I am wanting to add rear ac to my 97 4runner. I don't need a ton of air blowing back but something would help. I live in Arizona so I know that my kids are hot in the back because it takes awhile for myself to cool down in front. Front will eventually be cool but I want to somehow put a vent back there so they have something blowing on them. I thought about running some duct under the headliner. Would splitting a factory duct work or that a bad idea. I don't need actual controls for the rear, just want it to blow when i turn the front on. Any help would be sweet. If I can't find any on it, Im gonna try it myself and I will post pics and stuff and hopefully it works. Alright later

 

There are two problems with trying to put a duct to the back. The first problem is their just isn't enough room between the headliner and the roof to put anything more than a inch or two thick.

This leads to the second problem which is static friction and pressure. The A/C blower in the dashboard doesn't have the power to handle the static pressure of a small diameter duct. You could close all the dash vents and only get a trickle of air out the duct to the back because most of the blowers power was being used to create the pressure in the duct to force what little air is coming out.

This is why most all vans with rear A/C actually have a second evaporator and blower motor located in the rear of the vehicle. Adding a rear evaportor to the 4runner wouldn't be a really hard thing to do just pretty involed.

The biggest hassle would be cutting into the refrigerant lines under the hood and routing them all the way down the vehicle and into the back of the 4runner where an aftermarket A/C evaporator/fan unit was located.

 

Ditto on Fog Runner. Might as well either use remote start or get some vent visor for your windows and leave them slightly open.

 

How about adding Plexiglas (or similar) behind the rear headrests kind of like a solid dog barrier? The system would then need to a cool a substantially smaller volume of space. Just a random thought. Also, have you tinted the front windows? How about a tinted visor for the windshield?

I used to live in Phoenix so I completely understand where you're coming from. We had a 94 Accord down there in addition to our 4Runner and that car was way worse than the 4R.

Now that I live in the PNW, the issue is cold.