Any newer auto's AC systems which don't automatically switch to external intake?

[SmellMyWort]

@Me_Billy

Upscale vehicles have “cabin air filters” which filter the outside air.

With that said, a “HEPA” air filter will filter allergens out of the air and is the best air filter you can buy, however they are quite large and car cabin filters typically would not filter that well.

So check around for upscale cars, ask if a HEPA air filter can be installed, and ask to SEE THIS IN WRITING on the manufacturer’s vehicle brochure. (Salesmen lie!)

Also note that used upscale vehicles can have a MUCH lower price than a new one. And upscale means Volvo, Mercedes, BMW, Lexus, and high end other cars.

Every car I’ve owned has had a cabin filter and none of them are the upscale brands you list. Even my old, econobox Hyundai had a cabin filter.

[NBYodo]

@ftg

Obvious reasons? Okay, what are these “obvious reasons”? Around here 9 times out of 10 the outside air is more humid than the inside air.

Speaking of defrost, but not recirc related. Another auto setting I hate is turning on the AC when I have the heat on when I turn the fan direction knob to windshield.

Nope. Heat alone will defrost. Plus the windshield then stays a bit warm and further fogging in reduced (as well as helping with any frozen precip landing on the outside). As opposed to when the AC kicks on, the windshield gets colder and foggy is enhanced once I switch the knob back to body/feet flow.

Air conditioning activated will dehumidify the air, speeding up defrosting. Airflow path is through the cooling coil (cooling and dehumidifying) then through the heater to heat back up.

[Magiver]

Any vehicle I’ve ever been in would default to outside air and AC for defrost depending on the temperature. Otherwise the car would fog up from people breathing.

If you’re serious about this then you need to locate the servo motor wiring(not the correct year) that controls inside/outside air and bypass it. It’s most likely an electric servo so you would have to find out what the necessary input voltages are.

Alternately you could add an old fashion choke cable. You would have to attach something like this near the air door shaft. And you would have to clamp an offset lever to the end of the shaft so the cable can move it. Unless this was easily accessible it’s almost impossible to do.

[TSBG]

My 2010 Prius will change the settings with asking my input. Last night I had it set to recirc/heat/dash blowers/moderately high fan. It changed unasked to AC/feet blowers/full fan. I changed it back to heat/dash; the fan dropped to about 1/3. I bumped the fan back up a bit. Then it switched to heat/feet/full fan (NOT a/c this time). I cursed and turned the whole thing off.