"The problem with doing nothing is not knowing when you're finished" - Benjamin Franklin

spida · Guru

RE: Open Windows V aircon

Mike C · Senior Member

spida wrote:
Just wondered about the air resistance with windows open.

Hi Spida the link I posted above has all that detail.

spida · Guru

Mike C wrote:
Hi Spida
If you want a technical analysis try this link
http://www.sae.org/events/aars/presentations/2004-hill.pdf

Thank you so much for that Mike - just what I was looking for. Would seem at a glance that travelling at around 80 - 90 with aircon on is only slightly worse than with windows down. Much appreciated smile

vk6tnc · Guru

In modern cars turning on the AC tells the engine management computer to go to "Fast Idle". This prevents the engine stalling under the additional load and generates more cooling to prevent the engine overheating.

rockylizard · Guru

vk6tnc wrote:
In modern cars turning on the AC tells the engine management computer to go to "Fast Idle". This prevents the engine stalling under the additional load and generates more cooling to prevent the engine overheating.

Gday...

The variation in rpm at idle when turning aircon on or off is part of the Engine Management System as stated above. I am fairly confident (almost positive biggrin ) that if you are driving along at, say, 1,500rpm at 'cruising' speed, and put the aircon on (or turn on 'climate control') there will be no reduction (or increase) in rpm on tach or change in road speed.

Conversely, if aircon (climate control) is turned off there will be no drop (or increase) in indicated rpm on tacho or increase in road speed. When cruising the engine simply maintains the rpm needed to maintain the speed - dictated by the weight of the right foot - (particularly these days with their computer management systems ECUs). It simply chooses whether to suck more juice from the tank or relax a little and leave more in the tank biggrin

I know with my vehicle, whether I travel at 88kph @ 1,900rpm 5th gear with NO headwind or a 40kph headwind the only thing that alters is fuel economy is impacted. The tach and speedo maintain the same indications.

Therefore, I doubt if turning the aircon on or off at a given cruising speed (rpm) there will be any indicated change in the tacho - albeit there will (may) be a change in fuel economy.

Cheers - John

buffy61 · Senior Member

Air con all the way for me.... I cant stand the noise of driving with the windows down!!!

Dougwe · Chief one feather

If you have a copy of 'The Grey Nomad's Guid Book' it tells a bit about this subject on page 16, item 7. Might be a bit of help and it's from our webmaster's Cindy and Jeremy.

spida · Guru

Thank you again to those who chose to give me a serious answer. I do appreciate your opinions and help.

thomas01 · Senior Member

May not be quite what you are looking for, but I remember watching an episode of Mythbusters where they compared fuel use while driving a car firstly with all windows closed and secondly with all windows open. Fuel used between the two tests was negligible. Using the aircon reportedly reduces fuel economy by minimum 10 per cent. Personal experience tells me it is more comfortable to use aircon. (By more than 10 per cent). You work it out to what best suits you.

Regards
Marilyn and Rob.