Not on my 2016 Toyota Aygo. A/C worked well but you really feel the effect on performance.

I'm surprised at this, we used to have a Daihatsu Sirion 1.0 (same mechanical bits as the Aygo), and while having the a/c on did make a difference, it wasn't that much.

I recall the results of a test that came to the conclusion that using air-con at low speeds around town will affect fuel economy to the tune of 2 to 3 mpg, but at motorway cruise speeds there was no noticeable effect.

Depends when that test was done - many modern a/c compressors are more efficient at part-load than older ones.

I recall the results of a test that came to the conclusion that using air-con at low speeds around town will affect fuel economy to the tune of 2 to 3 mpg, but at motorway cruise speeds there was no noticeable effect.

I remember hearing an average figure of about a 5% loss in power, which presumably for your average C-sector car translates into about the figure you quote for mpg when driven the same with and without the A/C on and no windows open.

The extra airflow across the A/C condenser when travelling at high speed will inevtably help the system reject more heat and thus reduce the load on the engine.

That mpg loss seems to match what I get in my 14yo Mazda3, which is a typical C-sector car. Newer ones probably fair a bit better due to improvements in the technology.

My usual rule of thumb was open all the doors for a minute of two when getting in the car in really hot weather, then all windows when first driving below 40mph (wind resistance to great above and would cost more in mpg than to turn the A/C on) until the temperature inside stabilises, then shut all windows and turn the A/C on - on auto on climate controlled ones, and max cooling & vent speed/recirc for manual A/C systems, until the temperature cam down to what you want it, then adjust and switch over to external air.

Here is my quote.

https://in.xero.com/0UjdEUhbvRr6ximEt7VHymkoXyARW7vEieyfS76P?utm_source=email

Maybe your car was a bit simpler but this effectively wrote my car off.

Maybe Elekie Doc would like to comment as he has been involved some time ago

Depends where you took your car was it a main dealer? My local indi did it in less than 2 hours and charged me less than 2 hours labour. He didn't charge me for a re gas though as he had done one at the beginning of the moth shortly befor the compressor failed.

Very generous and honourable of them. Kudos to your local indie.

Very generous and honourable of them. Kudos to your local indie.

he believes he's reputation is worth more than a quick profit.

Good reputation = almost no advertising needed, as satisfied customers recommend them to friends and family. A pity many other businesses (especially some long-standing ones on the high street) don't take that attitude.

Is this quoted 20% figure from the same green source that is wheeled out from time to time that TV's use 10% of their power on standby? - utter rubbish.These sort of figures may have been closer to the mark decades ago.

It was possibly true back then - but cars (and TVs) improve over time

Majority of TVs don't come with an off switch nowadays just the power button on the remote. I can't remember what the quoted stand by power consumption of our TV brought in 2018 but I remember it being miniscule something like a few wats.

Edited by dan86 on 05/07/2020 at 07:55

A bit more background on the BIG AMERICAN numbers.

https://www.fueleconomy.gov/feg/hotweather.shtml

"Under very hot conditions, AC use can reduce a conventional vehicle's fuel economy by more than 25%, particularly on short trips. The AC's effect on hybrids, plug-in hybrids, and electric vehicles (EVs) can be even larger on a percentage basis.""

The sources given for these BIG AMERICAN numbers.are:-

1. Huff S.P., B.H. West, and J.F. Thomas. 2013. Effects of Air Conditioner Use on Real-World Fuel Economy. SAE paper 2013-01-0551 (doi: 10.4271/2013-01-0551). SAE 2013 World Congress, Detroit, Michigan, April 2013.
2. Lohse-Busch, H., M. Duoba, E. Rask, K. Stutenberg, V. Gowri, L. Slezak, and D. Anderson. 2013. Ambient Temperature (20°F, 72°F and 95°F) Impact on Fuel and Energy Consumption for Several Conventional Vehicles, Hybrid and Plug-In Hybrid Electric Vehicles and Battery Electric Vehicle. SAE Technical Paper 2013-01-1462 (doi:10.4271/2013-01-1462).
3. Thomas, J.F., S.P. Huff, L.G. Moore, and B.H. West. 2016. Measurement of Vehicle Air Conditioning Pull-Down Period. ORNL/TM-2016/275. Oak Ridge National Laboratory, Oak Ridge, Tennessee.

You dont usually get free access to SAE papers but the Oak Ridge lab paper is accessible. Its focus is on the pull-down period (cooling on startup after parking in the sun) but some data on the cruise phase is also given.

"From the previous study [1] the additional fuel use due to running the Ford Explorer A/C at 100% duty cycle is ~0.2 gal/h at idle (a 55% increase) and ~0.4 gal/h at 40-70 mph (an increase of 27% at 40 mph and 14% at 70 mph). For the Toyota Corolla the incremental fuel consumption was ~0.13 gal/h at idle (60% increase) and ~0.17 gal/h at 40-70 mph (representing a 22% increase at 40 mph to about a 9% increase at 70 mph). "

The cars used are not huge by US standards (huge cars would presumably do better on a % basis, and vice versa) or, at 2009, old by mine, but they won't incorporate the latest alien free energy technologies

The BIG AMERICAN numbers thus seem valid in context.

I'd guess part of the reason for the difference from the anecdotal UK experience reported above is that it does actually get quite hot in some parts of America.

I wonder how much of a difference it makes to have climate control (automatic A/C) instead of bog-standard manual A/C? My car has an 'Eco' setting that it regularly uses when the climate control is on 'auto' mode, only using the non eco setting when it's REALLY hot inside and out for the first few minutes to cool the car rapidly (including using the air recirculator), then reverts to eco (and outside fresh air) to maintain the desired internal temperature in all but the hottest outside conditions (normally into the 32degC range or so).

I think climate control makes all the difference the swift i had before had manual ac the sx4 and the other cars iv'e had alongside have all had climate control ore duel zone climate and have regulated the temperature in the car automatically and for the most part once it gets to temperature in the car slows down the blowers so maybe this is the reason for improved fuel consumption over standers ac.

Indeed - it's one of the reasons why I was glad I managed to get my car in the grade it is - I originally was looking at the next grade down at dealerships/brokers which only had manual A/C, so jumped at the chance when one with climate control (next grade up) was offerered at Motorpoint for £1k less than the cheapest broker's price.

Its an option that is worth every penny in my eyes, I set it to 19 and leave it there all year round no fiddling with buttons or dials cool on a hot day warm on a cold day and always just right.

In 1985 I took delivery of a brand new Honda Accord. It had a 1.8 12v petrol engine and was quite nippy and frugal. The kit on it was marvellous, I can't think of another gizmo I would have specified myself. The attractive item was the A/C of course. Very rare in those days for a production car. Absolute luxury and I have never had another car without it, either company cars or private. Never really noticed a reduction in power or consumption and as cars became more powerful and more efficient the less noticeable it was to be. I was told early on that it was more efficient run the A/c, later climate control, than have the windows open and the fan on full blast. Also to run the A/C all the time. Worked like a charm and never had trouble with any unit. Tried my last Skoda Superb on the Econ setting for a few weeks but saw no difference in power etc so went back to the usual climate control all the time. The wonder back in the 80's of sitting in a traffic queue with the windows closed when all the others were hanging out of their cars sweltering. I got some funny looks. The real pleasure was on holiday in France or Spain with the kids. Nice cool kids are not as fractious as hot sweaty ones! Worth every penny if it costs more to run.

Cheers Concrete

Cool air in hot weather is great, but I think I appreciate the rapid demist in cooler weather as much as anything.

Indeed - I loved my old 90s Micra, but the heater didn't warm up that quick and it had no A/C at all.

In really cold conditions in winter, I had to spend ages pre-warming the car up and had to keep mucking about with the air recirc button to keep the front windscreen from either re-freezing or steaming up.

In hot summer weather, I sweltered, and I was one of the more lucky ones, as the car had openable rear quarterlights (3dr only) and a tilt/slide sunroof with a very nice heavy-duty louvred screen to allow air through without letting much sunlight in.

My Mazda's auto function on climate control was a revelation. All I now do is change the desired temperature in summer when I get in the car so it doesn't cool down too rapidly (thermal shock) on a longer trip and adjust it back to a normal 'comfortable' temperature after about 10 minutes, doing the opposite when I get near my destination, occasionally switching to recirculated air and back again if in a traffic jam/polluted area.

I let the car's computer do the rest, and it seems to work very nicely. Occasionally I go the 'jack the heating up to max' if the air starts to smell a bit musty to kill of any bateria in the air ducts.

I'd rather forego a few mpg for a comfortable cabin - far better to drive in, and helps safety.