Keeping dust out of your vehicle.

[D4D]

I was chatting with a few people the other day and each had their own idea of the best a/c setting to keep the dust out. One idea is recirc setting with fan on to build up pressure, the other idea is fresh-air setting with fan on full. I use the recirc method but do find a get a load of dust inside when I flick back to fresh-air.

[shrek4]

It is my understanding that fresh air is best as it keeps the cabin pressure constant. Further, the recirculated setting should only be used for short amounts of times. Studies have been shown that the CO2 levels can rise drastically with the recirculated setting on after a 30min time. Thus, the driver feels tired and not as quick to act in an emergency situation.

[Teabag]

Fresh air minimised dust as it pressurises the cab. If you go to recirc you create a negative pressure in the cab hence allowing more dust in the cab......I only ever use recirc for the first 5 mins after the car has been sitting in the sun for some time, cools the car quicker. Other than that, I don't use recirc.....

[Black Diamond]

Dust finds it way in somehow regardless. I Always thought that fresh air would essentially let the 'Dusty fresh air' in so I usually leave it on recirc  with the A/C on.
Might try the other way and see if there is any difference

Bd

[evolution]

Im pretty certain that your car has an internal filter or "pollen filter" as standard from toyota. So even on fresh air you shouldn't have too much dust entering through your AC vents.
Its worth looking into as they are normally dead easy to change and great for really dusty roads.

Cheers
Evo

[champin]

There must be something to that 30 minute time limit for recirc air. I used to operate a German crane and a buzzer used to go of after 30 minutes on recirc.

[D4D]

OK so it looks like fresh air is the go, now what fan speed?

[fuji]

All I know is that in the old Prado fresh air let in the dust. So after the GRR last year we always kept the recirc. How about a fan from a computer and reverse the wiring, wedge in window and turn on when driving to suck out any dust that comes in?

[ras]

Champin..
I think the 30 minutes buzzer is to make sure that some fresh air, is pushed into the cabin... I seem to remember a commodore  owners manual saying not to run in recirculating mode too long, I assume due to stale air, and possible lack of oxygen...
It was a VT commodore.
Ras

[idlegossip]

OK so it looks like fresh air is the go, now what fan speed?

Hey D4D,

Have a look in your owners manual Toyota actually recommend it be set to fresh and from memory full pelt. I always ran it on recirc and use to get heaps of dust in until it was pointed out to me by the Toyota dealer after complaining about the amount of dust I use to cop.

[morcon]

When we did Cape York a couple of years ago (in a 120 Prado) we started off on recirc and changed to fresh after almost choking for half a day. When running on fresh it didn't seem to make any noticeable difference what fan speed it was on - we just ran the speed we wanted to keep the cabin temp comfortable.

[GU_Thomo]

I have found that the most successful system fo us is to use the fresh air setting and if a vehicle comes torwards us turn the aircon to recirculating until we have driven out of the dust from that oncoming vehicle, then switch back to fresh air.
Of course never follow in someones dust cloud.
This system keeps the cabin with positive pressure and also means you are not sucking dust through the front vent.
After 15,000K of mostly dusty dirt roads, on our last big trip, there was only a light film of dust inside the Patrol.

Cheers
Parry

[Chris-Vi]

We run our air on fresh to keep the dust out. We noticed on recirculating we good more dust in due to reduced pressure. Fan speed doesn't seem to matter. Sucking the air in from outside just pressurises the cabin. On our last trip we had a little dust down the drivers side on the back door so was happy with that. 

[chester ver2.0]

Fresh works for us but only if there is NO cars in front

Once you are taile end charlie you need to go to recirc

[Matto]

D4D,

For the Pathfinder, if we're not following anyone and not passing any oncoming traffic, then either one works for us. As soon as there's any dust in the air though, we've got to go to recirc otherwise the cabin fills up. I used to do the "leave it on fresh and turn the fan up high to pressurise the cabin" trick, but found that it easily results in much more dust inside the car. Recirc stops it coming in almost completely.

Our car doesn't come with an in-cabin filter as standard, but I've got the part numbers from the JDM model if I want to install one. I've not done it yet. I suspect a clean cabin filter would help massively once dust did get in. Of course, you'd need to keep cleaning/replacing the filter...

<Opinion with absolutely no supporting evidence offered>
I find it hard to believe that any car is perfectly airtight, especially once it's travelling. You'd never be able to open/close the doors, and if you drove up a mountain you would blow a door out. So I think the likelihood of being able to create dangerously high levels of CO2 inside a car simply from breathing would be amazingly difficult, lest of all time consuming given the volume of air involved. I'm not saying the aforementioned crane doesn't have a 30 minute buzzer for recirc mode, my gut feeling is simply that that is a very conservative time limit, and for a much lower internal volume of air.

Likewise, I doubt the ability of an AC fan or a simple ram-air effect would be sufficient to actually raise the pressure of the air inside the cabin such that it would actually make a difference. Otherwise if you changed your AC from recirc to fresh, you'd feel your ears pop as the pressure rapidly increased.

I suspect the different experience people have is more due to the different cars having their external vent intakes in different positions. IE, if one vehicle sucks air from the base of the windscreen, that's a relatively high-pressure area that has relatively static airflow. If the vent intake is inside the engine bay, it may be in a lower-pressure stream with a high flow-rate that's more susceptible to loading up with dust. My theory is that given these different vent locations, different cars will behave differently on fresh or recirc modes, and owners will have better success on either.
</unwarranted opinion>

Cheers!
Matto

[LC]

I have found that the most successful system fo us is to use the fresh air setting and if a vehicle comes torwards us turn the aircon to recirculating until we have driven out of the dust from that oncoming vehicle, then switch back to fresh air.
Of course never follow in someones dust cloud.
This system keeps the cabin with positive pressure and also means you are not sucking dust through the front vent.
After 15,000K of mostly dusty dirt roads, on our last big trip, there was only a light film of dust inside the Patrol.

Cheers
Parry

I agree with and pretty much do the same as Parry, the only problem I have is I usually forget to put it back to recirc when a vehicle comes the opposite way. Particularly if driving somewhere where the scenery is good.

[doc evil]

I use fresh........

The best "check" is before you hit the dust, put your fan on the highest speed (must be highest speed to keep dust out), try fresh and either crack the window a smidge, you'll hear the air rushing out or alternatively, jump outta the car and shut all the doors. Put your hand under the door handle or near the black vents behind the bumpers etc. You will feel the air coming out. if not, try recirc.

Either way, there should be air coming out. This dust proofs your vehicle.

Doc.

[KingBilly]

I'm with you Matto.  There's no way on earth that you will die from CO2 poisoning by driving around all day with your vents on recirc.  All cars have exhaust vents at the rear and they can't be closed.  Most (and without any authority I would hazard a guess that all) modern vehicles draw some air in through their dash vents even when on recirc.  My Subaru does, my wife's Diahatsu does, my previous Camry did, my work Kluger does.  To test, try putting the air onto recirc with no fan on a cool morning whilst doing 100k.  Bet the middle two vents have some air coming out of them.

But I have been wrong and happy to be proven wrong again.

KB