Why does manual state "only temporarily" allowed to drive with Ac and Heat off ?
 

My manual states this about the Off button on the HEAT/AC...

"In this setting, the fresh air supply to the interior of the car is shut off,
(to prevent enterence of odors, ie: while driving through tunnels etc. or to prevent the enterence of water from automatic car wash). Use this setting only temporarily while driving."

Is this simply so I don't suffocate?

Why can't I drive around without heat blowing on me in the summer?
(besides that my AC dosent work)

Will leaving it off damage something?

I think its just so you keep the cabin ventilated. I've left mine off for a long time when I was driving around with the windows down. It won't hurt anything.

if it totally cuts off the flow of air to the cabin, then it most likely says that in the manual to cover the lawyers butt... that way if you die of carbon monoxide poisoning, then you can't sue... because you should have read the manual.

I assume they are saying that the climate control system is intended to operate all the time, but can be turned off when necessary. Driving with it off will not hurt anything. I just leave mine on all the time so I don't have to think about it. If you open the windows, or your AC doesn't work, you might as well shut it off.

The manual for my '96 says to not shut it off for very long to prevent fogging the windows.

Good point, the AC does a very good job of keeping the windows clear, especially when the heat is running during cool/wet weather. I once drove half way across the county in those conditions (about 50F and rainy) with broken AC and having the window fog up was a real PITA, nothing worse than being trapped in a car with damp heat.

Your supposed to keep it in EC to keep all the little flaps and stuff working. I guess they don't like to sit for long periods of time.

Knock on wood I have never had any issues with that part of the system.