A/C efficiency penalty quantified

[Peter7307]

Originally Posted by drmiller100

I would really appreciate some real numbers from the real world from real members on this site.

For instance, vehicle weight, vehicle size, mileage with AC and without, and city or highway driving.
Thank you much.

On my vehicle the fuel difference is about 0.5 ltr / 100 klm for air on and off.

Steady highway running is around 7.2 and with the air on it is around 7.7 l / 100 klms. (US mpg: from 7.2 (32.6) to 7.7 (30.5) so about 2 mpg) at around 90 kph (US 55 mph) which is just under the legal max of 100 kph (62 mph)

The car is a GM variant (Holden 2003 Acclaim sedan) with the 3.8 engine and the 4L60E trans. Weight is around 1600 kgs (3200 lbs US approx).

Peter.

[mcrews]

I would really appreciate members posting there vehicles under their avitar.......

just sayin.....

[Ladogaboy]

I almost never run my A/C anymore, but when I did, I only noticed about a 2-3 mpg (10%) decrease.

At this point, I've mostly weened myself off of using the A/C. We've had a pretty mild year, and in addition, my car is white and most often parked in the shade. I'm thinking I might get a UV reflective tint at some point, but I haven't really needed it yet.

[Frank Lee]

Should I drop a note to the lab telling them they are full of crap?

I don't use a/c enough to get any data.

[Tesla]

Just did a big trip, about 3,000km, air con on all the time, 30-36C outside, virtually no change in the FE.
I think this is an issue that shows up more with smaller vehicles, mine is a big diesel 4x4, smaller vehicles still have the same needs for auxillary load, whether it be alternator, aircon etc., but as a percentage on the fuel economy it is much bigger on smaller vehicles than on a larger vehicle.
I could delete all my auxillaries and not see much change, but if I keep the weight down and streamline the box, I can get major improvements.

[gone-ot]

...I've "measured" drops in MPG ranging from 10% to 14% on my Vibe with A/C, but back-to-back A-B-A testing was NOT exactly 100% "repeatable"...LOT's of variation.

...hence, I 'rule-of-thumb' A/C at 10%-15% for my car...others will obviously get different values, but probably close.

[euromodder]

Originally Posted by Frank Lee

Should I drop a note to the lab telling them they are full of crap?

Nah, it's just that the cycle during which they measure these differences, isn't representative of normal everyday driving.


The problem I have to filter out the AC use, is than I mostly use it under conditions that don't make up most of my normal driving.
When the AC is on, I'm usually also carrying passengers - and when carrying passengers, I'm usually also driving faster, both of which affect FC.

[Peter7307]

Originally Posted by Tesla

I think this is an issue that shows up more with smaller vehicles... smaller vehicles still have the same needs for auxillary load, whether it be alternator, aircon etc., but as a percentage on the fuel economy it is much bigger on smaller vehicles than on a larger vehicle.

Tesla,
Thats is my thinking as well.

I remember my brother's Nissan Micra had aircon and you could have cool air or more performance...but not both at the same time.

Interestingly he traded to 4.0 litre Falcon and gets about the same economy.

I suspect he doesn't have to drive the Falcon nearly as hard.

Peter.

[niky]

For really small four-pots and three-pots I've had and tested, it seems to be about a 10-15% penalty in traffic, depending on how weak the engine was and how big the compressor was.

We did this on the dyno (a hell of a long time ago) and got about a 10-15 horsepower drop on a standard 1.6 liter engine at idle... which just happened to have 400 horsepower and a turbocharger, but it's the same for most small engines... and the turbo didn't make boost at idle.

Worst I had was a compressor conversion when the Calsonic compressor clutch on my Nissan went kaput for the fourth time. Stuck a bigger compressor with an indestructible rubber clutch on it, instead... on there and you could feel about 25 to 30 ponies go south every time it turned on.