My current 1.9Tdi ( soon to be replaced by a 1.8Tsi Scout ) is the only car I’ve ever owned where I don’t feel any impact from having the aircon turned on. This includes a 3 litre Supra. I pretty much leave it on all the time.

Whats the general consensus on this ? On all the time or just when you need it ? I’ve also not noticed a real impact on fuel economy with having it on all the time.

Am I likely to notice a difference with the 1.8’s driveability if I have the aircon all the time ?

I can't notice any difference in mine.

The A/C in the O2 seems just right, I am able to leave it on without noticing any MPG difference or feeling dessicated.

the pump always turns to keep some AC gas/fluid circulating to lubricate the seals.

If you have it on ECO it runs without compressing but still runs. I Notice a couple of mpg difference with it on or off but some of that is probably due to the fans running faster too.

I have it on ECO in the winter and just leave it on in Summer.

I'm on my 4th diesel Octavia and I've never noticed any difference with it on or off on any of them. This includes tests such as driving 100 miles out on a day trip with it on and returning with it off, comparing whole tanks and also short tests such as sticking cruise control on a flat road and comparing off and on.

Now I know there must be some extra fuel being used, you don't get anything for nothing, but I am saying I cannot detect the difference.

This flies in the face of those people who are always telling people to turn off their aircon because it's killing the polar bears or something.

I think I learnt the hard way, I had mine on ECO for just over 2 yrs, did use AUTO a few times when it was hot. Eventually the compressor died, this may not have been related. Got another compressor and now I leave it on AUTO all the time so to have the system pressurised most of time.

If I'm driving along in my Octavia at a steady speed on a flat road on a calm day, and switch on the AC, there is a noticeable reduction in speed and the mpg readout on the dash drops by a few mpg.

If I'm driving along in my Octavia at a steady speed on a flat road on a calm day, and switch on the AC, there is a noticeable reduction in speed and the mpg readout on the dash drops by a few mpg.

Thats odd. Like I said i've never noticed even the slightest difference on our 1.9. On our old 1.4 Fabia it would almost stop when the aircon was on ! I live on a hill and the car would not pull away unless you turned the aircon off.

It was a real pain.

Never noticed any difference in my old Octy PD140, was left on Auto for the nearly 4 years I owned the car.

Aircon is not just for summer, its also handy in the winter as long as the temp is above 4c. During the winter the AC removes moisture from the air, so the interior does not steam up so readily and any condensation on the inside of the windscreen clears very quickly. Below 4c the AC is deactivated to stop the system freezing solid and protect the compressor. The heater comes after the AC system, so the car just heats the airconditioned air instead of fresh air.

The compressor is a variable displacement type so it pumps according to demand. On a hot day with the a/c cooling hard you would notice the difference (takes about 7HP). On a cooler day it will running at a low pumping rate and you probably wouldn't notice it.

Mine is left on auto, never noticed any difference in mpg off or on.

Yesterday though, the aircon kicked in big time and cold air poured out all the vents- even the middle dash ones which rarely do anything on auto.

The car was quite warm when I got into it .

I leave mine on auto all the time too, so don't really know what the difference is mpg's wise !

I hoped this would extend the life of the compressor, but if the AC is shutdown below 4 degrees, then I guess its been off for much

of the winter...... It now hisses and not alot in the way of cold air comes out now. :-(

I'll try the diagnostic setting to see if the compressor is running, but I ain't heard it for a few weeks now. :-(

I'll try the diagnostic setting to see if the compressor is running, but I ain't heard it for a few weeks now. :-(

If its working properly you won't hear much. With the engine running and the temp set to low, feel the outlet pipe running from the compressor to the condenser - it should feel warm-to-hot (depending on ambient temp).

According to Mythbusters it is more economical to use A/C above 50mph than it is to drive with the windows down.

My experience with two 1.9TDi's was that there was no noticeable difference in acceleration or fuel economy. My current 140PD is just the same.

I've heard that some cars disengage the A/C compressor automatically while under full throttle. I'm not sure if this applies to the Octy2 but I suspect it might.

I leave mine on all the time - can't say I've noticed any difference on the few occasions when I've turned it off. Still going as well today as the first day I had the car. I had a Ford Escort years ago and the a/c packed up after a year and a half.