I'm pretty sure that it's a door that opens to the cabin interior. In other words:
open: drawing in cabin air, recirculating it.
closed: drawing in outside air.
(as always, YMMV)

As I said before, the temperature setting has no effect on the recirc door. Only the air delivery selector.

In the summer, after your vehicle bakes in the sun, the cabin air is hotter than outside air. So recirculating that hotter air is going to keep it hot longer.

 

Also, if where you are the temperature gets cold in winter and when the relative humidity is quite high, there might be a high risk of fogging your windows all the time if there is not enough cabin air circulation. This is dangerous.

I wonder why you have so much exhaust smell in your van ? If I remember correctly, rarely I can face this kind of situation. Maybe once or twice a year when following an old car for a couples of minutes.
Like mountainmanjoe said, are you sure it is not an exhaust leak ?

 

I don't smell exhaust unless I'm following and old/smoky car or sitting in dense traffic. Alot of the cars in my area are old/sh!tty so I'm dealing with more exhaust smell now than I was a few weeks ago. In my last town, most of the cars were newer and I rarely smelled exhaust. I never smell exhaust when I'm on the road with no other cars around, either moving or sitting still. I have also spent many hours working on this van - it's definitely not leaking exhaust. And it's not that there's a huge amount of exhaust in the van, I just don't like any at all. This is the first car that I've had that I had to deal with this. I've always lived in dense areas and always kept the AC on recirc to avoid bringing in traffic exhaust into the car.

 

I think this is where my confusion is. I assumed that if I put the control on MAX, it would make the compressor run. I haven't tried MAX with heat, I've only been using MAX for AC and the vent setting for heat. I will try it today and see if the compressor runs or not. This may all be my own stupidity

 

You are still a bit confused. The compressor turns on in these modes, regardless of the temperature setting.




If you turn MAX with heat, then the compressor will run. It does this to dry out the air for two reasons:
1. You cannot blow moist air at a cold windshield. The condensation will quickly obscure your vision
2. It takes less energy to heat dry air then moist air.

The operation is described in your owner's manual.