Why a cabin air filter?

Exactly. Its the same purpose as a house ac filter. If filter is removed won't take long before the evap coil under the dash gets clogged. In fact its a very good idea to at least once a year clean the evap coil under the dash.
Just like you should do in your house.

Toyota parts counter sells a 2 aerosol can kit with a special hose. One can is foamy microbial cleaner. The other can is perfume. Comes with special hose as a kit. $25.

You attach the special hose to the cleaner can and then under the car attach that hose end to the ac evap rubber drip hose. Thats the hose all the water comes out of when the ac is running. You shoot the entire contents of the foamy cleaner back up the drip hose. It fills the evap box. Remove the can and it will turn to liquid and drip back out the hose onto the ground.
On a Gen II you can also pull back the carpet on the pass side up under the dash and that drip hose is right there poking through the firewall. Not sure if its exactly there on a III though.
The perfume can is supposed to be shot into the air dam at base of windshield while ac on but its really old lady perfumy so I never use it. Its disgusting.

Have down this 3 times on my Gen II in my driveway. Very very easy. AC smells 100% better. It keeps the ac evap box clean and most importantly keeps the condensate drip hose clean and prevents it form being clogged. Gets clogged from gunk when you don't use a filter. Dealer is $100.

I usually do it every time I change my trans fluid.

To the OP:

Always use the AC. Always on recirc because then your using the filter. Its colder drier air. Keep the cabin as dry and cool as possible to protect the millions of electronic connections in the cabin, the Hybrid battery connections and to keep the Hybrid battery cool. Buy the black charcoal factory filter lasts way way longer that the regular white filter. eBay or online.

If filter is moldy that means the cabin is moldy. Filter is on intake of e-coil so mold is coming in to ac system. Cabin is very damp. That's bad and not right. Means the cabin electronics is being exposed to very high moisture=Corrosion.
Poke around and see if any wiring connections or the chassis metal is getting rusted. I would address that. If not you will eventually have an electrical gremlin intermittent connections nightmare car.
Check in the spare tire well for water you may have a leak and there's water in the trunk.

 

The filter is always used, period. Doesn't matter if its outside or inside air.

 

You're using the filter either way, but if you force it to be always on recirc you're running the risk of making the system moldy. It's best to use Auto as it does a good job of switching between outside air and recirc when appropriate (unless you live in a climate where Auto forces it to be in recirc the vast majority of the time).

 

How does it get moldy always in recirc? In fresh air the filter see's alot more humidity than in recirc. In recirc the air is much drier becasue its conditioned.

Now when you shut the car off you should switch to fresh to let the box vent to outside.

 

Hehe, I believe you mean riddled, not ridiculed.

SCH-I535

 

Now that you mention switching to fresh when shutting off the car, that's not technically leaving it in recirc 100% of the time. Another way to do it is what Tideland suggested, which is running the fan for a few minutes with the A/C off before shutting off the car.

 

Prius HVAC also has a humidity sensor.

 

I don't think it's so much the filter as the whole ventilation system: Any time you switch off A/C after using it for a decent time, you'll get a "dump" of moisture. Depending on conditions, that could start growing mold.

 

Cadillacs have a set-up where after the car is shut off, the HVAC blower will run about 10 minutes more to dry the evaporator core.

 

I've noticed that in ECON mode the AC will start off in recirc, but after awhile it will change to fresh air, then it will go back to recirc again. I guess that's the humidity sensor at work.

 

That's my guess, since recirc is more efficient.

 

Glen 20 gives me asthma. 99.9 % of 1 million leaves 100,000 resistant bacteria to reproduce. Widespread gratuitous use of antiseptics is stupid.

 

as a fellow Asthmatic I can empathise with you, but I was far from suggesting spraying the world with it, perhaps you can suggest an alternative ?,
p.s 1 million - 99.9% leaves 1000, your comment on soccer is correct though

 

Yo, guys,

Edthefox told us about the Toyota antimicrobial product that cleans out the drain tube while it's killing the little beasties living in the swamp of you evaporator area.
The air filter keeps the organic dust and such out of the evap, but if and when the green stuff starts growing there, the drain tube can get clogged with that crud. It is important to confirm that your AC is draining water freely.
There should be a slight flow of air and cold water coming out of that tube when the AC is on the the fan is high.

Just to drag this up again, ,, What do you asthmatics think about the "Microfilter/Ion Generator" some (or all?) of these cars have? You know there really is no "microfilter" in the system, right?
Is it true Ion Generators can be an asthma trigger?

 

Had to look it up as I had never heard of it, in short there is no "Microfilter/Clean Air button" on the Prius C in Australia

 

Doesn't look like the C has it in the USA either.

 

Its nothing more than a programmed 3-min cycle of recirc mode on the blower.

 

Are you asking about the Plasmacluster ionizer (found only on the Four and Five but discontinued in 2012+) or the Dust and Pollen filtration button found on all trims?

It also switches to 100% recirc instead of the usual 80% recirc. Really helpful for passing through dusty or smoggy area as no outside air gets in.

 

And turns on the A/C compressor.