Internal or External mode of air circulation in the AC

I got my SX4 teflon coated (entire pkg of teflon coating, under body anti rust coating and engine lamination) and after that I started noticing a noice coming from the ac vents. On closer examination I found that it was coming from the blower. I took the car back to rohan motors and they told me it is because of some leaves etc. which is stuck in the front side. They cleaned it up within 5 - 10 minutes and did not charge me for that.

They asked me to to keep the AC mode to "internal circulation" (not sure if this is the term used, but to keep it in a mode that reciculates the air inside the cabin). His point was that such particles can get stuck agian if I keep it the other way. I know that by doing this AC becomes more effective but I mostly keep it the other way to avoid any stale air in the cabin.

My question is, is there any other reason why one should stick to either of the two modes, Internal air or external air? if someone can share specific cases or real life examples it would be great. I have read a few cases of people dying inside the car when they kept the windows rolled up and the AC was on. I am sure that the AC would be re-circulating stale air with less oxygen and more CO and CO2. Correct me if I am wrong.

Hi,

Never keep the internal air circulating for more than 5 min. Actually the mode is to get faster cooling - it takes only about 5 min for the cabin to be completely cooled - after that you are supposed to shift into the external air mode.

I am a bit surprised at it, but leaves !!!! That is quite shocking - I hope the guy understands that there is a grill on front of the car and the purpose of the grill is to stop leaves or anything as big as leaves from comming in.

Anyway, try checking the specific area from where the guy has taken the leaves off on a daily basis and then see if the problem persists.

Never use the internal cooling mode for extended periods - it is not good.

Regards,

K Prasad

Thanks for the prompt response.

Yes Leaves,

He took out the glove box completely was able to remove some small leaves etc. by his hand only from behind the glove box. I dont think I can do it on a daily basis but if I hear such noise again then I will try to open the glove box myself.

I too find it hard to believe that leaves can enter under normal running. I think that during the engine lamination or under body anti rust coating they might have kept the vehicle open and some dry leaves might have got in.

This air re-circulation feature is i guess a very under estimated & under utilized one. I for one, as a common car commuter, would believe that switching re-circulation would be the better option.

I have also seen that when we switch the AC off but keep the blower running then we have the stale smell of moisture in air. Also i think by keeping AC on (with re-circulation ON) for long journeys always, there is no point served. After sometime the air becomes unhygenic and beyond a certain point the temperature is already at the lowest so the AC would not be that effective too.

Also i think while going on drives it would be better to switch AC on while in 3rd or higher gear so that we could derive better mileage. I am sure more experienced owners could add to this.

Bhushan

To my understanding based on personal experience (substantial on highway/long drives)....

AC should be generally used with re-circulation OFF but it should be switched ON at a regular interval of 45 minutes or so for 10/15 minutes OR, in other words, it should be ON for 1/4th of the time/journey. This enables circulation of fresh air & keeps the cooling very effective too.

Yes, use of AC should be avoided in lower gears (below 3rd) for better mileage (& performance).



Honesty is not a Spare Wheel that you pull out when in trouble. It's a Steering Wheel that keeps you on the right path throughout the life's journey.

not more than 5 minutes in internal circulation..? Dont think so prolonged recirculation can lead to mild asphyxia thats all.Recirculation is MORE EFECTIVE and gives better mileage!!

If there was a health hazard  associated with the re-cir mode dont you think the same would be given as a warning in all the car manuals..i have yet to find anything like that.Also the smog in most cities would turn out to be more harmful that the re-cir air.

Most advance HVAC units use about 60% recir and 40% external air modes.

Yes, I agree.  In fact, even 40% is on higher side - actually not required to that extent. My experience, as stated before, says that the re-circulation mode should not be used more than 20/25% - more than enough.  

I have tried different variations in the quantum of usages, and have experienced that even if it is used to the extent of only 10%, it's fine.  But the best/optium usage of re-circulation mode is 20/25%

Honesty is not a Spare Wheel that you pull out when in trouble. It's a Steering Wheel that keeps you on the right path throughout the life's journey.