I can see the value in this system, but I'm not very trusting of electronic hydrometers--I think they'd be the failure point in the system. Also, when it's rainy, just changing outside air for inside doesn't guarantee less humidity--it's already raining--humidity is 100 percent for both. Unless you run the AC (to use the cold evaporator to remove humidity, like a real dehumidifier), you don't have a sure-thing.

I'm really in favor of a system similar to that that you can turn on when you're not present that would keep the temperature from getting too hot by running the existing fan when it's above 110F. This would prevent your dash from cracking early and make it easier to cool when you do get in. I'm presuming that the car already has air-exit-vents for the hot-air in the trunk--most cars do.

Yes, a climate-control fan. hrench - your post raises 2 points for me. I drive the car with 3 people in it who've just been in the rain themselves with waterdrying off all their clothes. The outside temperature is 5 degrees C. We drive for 20 minutes with the heat/AC on in the car. The car is filled with moist warm air. I park the car, everyone gets out, despite attempts to air out the car, the relative warmth causes condensation on the car's inside after it has been parked. If the fan simply vented the heated-moisture-laden air and replaced it with cold moisture air, the condensation would be much less.

I like your hot-car idea - in cold weather, i often leave my dog in the car in places where security dictates no windows are open when it is parked. The car is cold, and the dog curls up on the seat for a nap. The moisture of the dogs breath condenses on all the windows by the time i return. The presumption that a parked car needs no climate control is from car companies - but in real life,after myself taking a nap in the car on a lay-by, a way to vent the space whenparked without opening windows begs consideration.

The fact that you and your dog do not suffocate when sitting in a non-running, parked auto is evidence either that air is being constantly exchanged or you're not parked for long. I'm guessing air exchange.

A lot of that road noise you hear when driving is air flowing around the seals in the doors. And if your car is as old as mine that's considerable.

I have a 2000 honda CRV - my solution has been to order up those vent covers that allow a window to be cracked without rain coming inside the car. I should have got them ages ago; That said - i'd rather that the car designers considered that people might pay more to have a climate control system that is not so noisy when its running full blast to dehumidify (the AC), and capable of moving seriously larger volumes of air for sensitive athsmatics and those who need air flow in the back seat... the climate control systems in cars always feel like cumbersome afterthoughts rather than the primary comfort givers to the passengers who depend on that atmosphere. (open windows in heavy rain, extreme cold, extreme heat, or extreme freeway filth) - require the climate control system be sharper... heck, i'd like one that would let me fit an oxygen tank, that it could supplement the oxygen to the interior of the car. Why don't they take the air climate control seriously - dehumidifying surely reduces mold and dust mites in carpets in cars just as well as in bedding.