Yes you can, a friend of mine drives a 2002 Honda Civic, the ultra budget model. His car came from the factory with manual windows and no AC.

 

Chevy astro vans had a nice vacuum powered valve for just such an occasion.

 

We had an astro with the 4.3 as I was growing up. It was a real trooper. Trips to the beach and God knows where else. We sold it to my dad's brother like ten years ago, he has 6 kids. And it just bit the dust last year or so.

Mom got it stuck in the ditch one time after we got caught out in a giant suprise snow storm but otherwise never had a problem.

 

Should one ask how you know said valve is good for such a task

But, hmmm, should one be adding yet another vacuum operated device to a system that is noted for vacuum issues?

 

I have an Astro Van. Although, I had to replace it once on the van.... (leaking) Wasn't that expensive... it's an interesting idea, not sure if the hoses are the same size, but, would be simple enough to check out.

 

Seems that GM, Chevy, Cadillac valve (74781) has 5/8" flowing to the core, and 3/4" return line.

Around $20.

There are other versions of this 4 Seasons Heater Valve... one is listed for a Jeep (74777)

Which looks like 5/8" all round.

The other is for Ford, Lincoln, Mazda, Mercury (47809).

 

If going this route, I guess a vacuum source that conveniently switches with heat 'on' would be good to tap into.

 

Probably need a separate switch for it, as the temp door is either cable, or electrically operated.

 

Something like this maybe?

 

Ooo, Perfect!