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-   -   Car A/C in fresh air mode? (https://www.team-bhp.com/forum/technical-stuff/94526-car-c-fresh-air-mode.html)

I recently serviced my car at MSM and was accompanied by a service advisor during the post service road test. As the current climate is not warm, I normally drive around with ony the blower running, with the AC vent in fresh air mode and windows rolled up. The SA noticed this and remarked I should always keep the vent closed otherwise lot of dust will accumulate in the cooling coil of the AC, necessitating premature overhaul. He said I should open the window for fresh air.

This got me a bit confused. Even during summer, when I go for long highway drives with the ac on, I periodically open and close the vent to allow fresh air in the cabin. Is there any truth in what the SA says? Can someone clarify?

He is sort of correct. Dust will also accumulate in the ac ducts and you will need to get it cleaned sooner than usual. Also, in the fresh air mode since fresh air is being sucked every time, your ac needs to work harder than usual to cool it. The in cabin air has already been cooled by it but you are letting it out.

It is a good habit to choose the fresh air mode for 10 mins once every hour if there are more than 3 occupants in the car to ensure that oxygen levels in the car and the air remains pleasant due to recycling else some people could complain of head ache etc.

Do you really do this !! i suggest please avoid doing this. You are suffocating/contaminating yourself slowly, but surely. You are getting in the pollutants inside the cabin. You are getting in the pollutants continuosly with the pollutants having no place to escape but to enter your body through your breathing. Its a very dangerous thing that you have been doing. Please stop doing this.

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He is right when saying this IMO. However, the overhaul will depend on where you are driving everyday, i mean if you are driving in dusty locations more often, you may have to go in for an overhaul soon.

This is a regular practice that everybody does. I also do the same thing on long drives.

^ agree to that.

With the "fresh" air mode, you are just getting in all the dirt and dust on the road. And in Chennai, I bet there is quite some of it!

The vents would gradually get clogged by dirt and leaves (I had a small one come out of vents in my car long time back!) etc.

Just came to my mind, instead of changing to fresh air mode, wouldn't it help equally if we just rolled down the windows for say a half a minute or 1 so that fresh air could come in (literally).

I assume your AC in not in the cooling mode with only the blower on; why put the extra load on the engine?

He's right, especially in city driving you will accumulate a lot of dust in the coil. Ideal way would be drive with windows open initially till you are on the main road, then roll them up and switch on the AC with vents closed.

Its fine if you are doing it on highways, just make sure you do not do it while crossing some dusty patch of the road.

Cheers!
S

I keep the circulation mode always off as allowing outside air allows smoke, smell of burnt fuel and dust specially in Bangalore roads. I just refresh the air inside car near my house where plenty of trees are there with fresh air specially in the morning time.
And yes if number of people are more in the car its good to keep on allowing fresh air periodically.
Even after following this practice i got cleaned my cars AC vents during last service at 18K kms costed me 1500 bucks.

Don't make a big issue out of this.
When you open your windows - you suffer the same fate.

And when you close your windows, and keep the air intake to outiside - it doesn't mean that outside air just keeps accumulating - if that was the case your cabin will explode after a while (because of high air pressure inside)!

Outside air mode simply means that outside air is entering your intake and then existing (very similar to recirculation mode - just that in recirculation - you are not taking-in any outside air).

Correct me if I am wrong, but is it not the compressor (AC) that puts the load on the engine, and not the fan! AFAIK the fan speed also has no bearing to the load on the engine!

I will advise the following:

1. In wet conditions or to defrost the windscreen the fresh setting is necessary.
2. If you want to use the AC and are finding it a bit too cool, then switching to fresh is another way of reducing the cooling.
3. When you park the car do remember to switch the vent to recirc (I am talking of manual/wired controls) and not electronic controls.

Hi Neilguy,
I agree. Thanks for the correction. I guess, i wanted to say 'on the electricals' (Although it would still be negligible).

Cheers!
S

Whenever the climate is cool I usually drive with the vent open and just the fan running. I keep the windows rolled up to reduce the dust and noise. I also open / close it from time to time on the highway when the AC is running.

But the SA says to use it is a sure shot way for premature overhaul of cooling coil and we should better leave the vent always closed. The manual just says to drive with the vent open if we desire fresh air in the cabin without the ac, and to keep the fan running / shut off as desired. There is no word about the harmful effects on the coil.

I am worried more about the coil than pollution inside the cabin, which will enter whether we open the vent or the window!

Precisely. Either ways (keeping the vent open or the window open) dust is attracted inside the cabin. I prefer the latter as it does not have an effect on the AC ducts and the cooling coil.

Having said that, I do switch to fresh air mode once in a while on the highways(where the pollution levels are relatively lesser) and never in the city.

In my car (Verna) whenever you switch on the Auto AC mode the fresh air mode is automatically switched on. In fact you cannot keep the Auto AC mode with recirculation also on. I usually drive in the recirculation mode as during traffic the fumes start getting inside the cabin and that is not a pleaseant feeling. The auto mode switches off whenever i am in the recirculation mode.

Anybody else has similar settings?

AC load depends on amount of 'fresh' air used, more the humidity in the air, higher is the load. That is why, most cinema halls throttle the fresh air to save money, which causes a minor headache.
When you don't need the AC and you are not on a highway at higher speeds, the better option is to keep your windows partially open. On the highway, it is better to close the windows, keep AC on recirculation without the compressor on or at temperature setting that is comfortable, and time to time for short periods go on fresh air mode if necessary. If you are taking a break to stretch your legs once in two hours or so as i do, the fresh air mode would not be necessary.

I have stopped using the "fresh air" mode altogether. You'll find my cars running only in recirculation mode, except for long highway drives where we'll switch to "fresh air" for 10 - 15 minutes (lighten up the insides).

Unsurprisingly, the air-conditioner is a lot more effective when running in recirculation mode.

Gansan : If you like driving around in "fresh air" mode, well...do just that. Don't worry about the cooling coil. What the SA told you is akin to "if you use the brakes, you will need to replace your pads one day" :)