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Air con knocked 10mpg off my economy!


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I have just been to South Wales for a week visiting family, on the way down (220miles) we had a really good run, almost no traffic but used the air con for the whole journey and only managed 56mpg. We came back today, a lot more stop/start traffic jams etc but no air con and managed 66mpg! A massive hit of 10mpg...I didn't think it would be that much of an impact.

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I have just been to South Wales for a week visiting family, on the way down (220miles) we had a really good run, almost no traffic but used the air con for the whole journey and only managed 56mpg. We came back today, a lot more stop/start traffic jams etc but no air con and managed 66mpg! A massive hit of 10mpg...I didn't think it would be that much of an impact.

 

Yep, AC does affect the economy - not sure what the difference is compared to opening the window a bit though (lessened I would imagine if deflectors were fitted), which is what I tend to do, barely use the AC or heating in mine at all

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2hp sapped while only using half your hp is not an issue is it?

 

10mpg seems a bit OTT to be honest, but if you have done a brim to brim then that will be what it is.

Was it more uphill going than coming back, and have you forgotten anyone by any chance?

 

??

Did you fill up while there and get some lovely lively perky Welsh Fuel?

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Have you also considered the relative heights above sea level of each end of the journey?

For example according to the Columbus my home is approx 400ft above sea level and my work is at 10ft above sea level. On a totally clear run to work (all motorway) I get around 65mpg.... On a totally clear run back home (same all motorway route as the journey to work) I manage around 55mpg.

I know the air con will have made a difference to the mpg but you'll probably find the total amount of downhill or uphill driving will have contributed more.

Sent from my iPhone using Tapatalk

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Some interesting theories, the road seems fairly flat all the way, M2, M20, M26, M4 to j28. I used the same fuel from the same fuel station, I didn't drive any faster or slower. I probably weighed more coming home as well!

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Some interesting theories, the road seems fairly flat all the way, M2, M20, M26, M4 to j28. I used the same fuel from the same fuel station, I didn't drive any faster or slower. I probably weighed more coming home as well!

 

Going against a prevailing wind will make quite a difference - saw a 6 mpg hit from a headwind recently.

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I have just been to South Wales for a week visiting family, on the way down (220miles) we had a really good run, almost no traffic but used the air con for the whole journey and only managed 56mpg. We came back today, a lot more stop/start traffic jams etc but no air con and managed 66mpg! A massive hit of 10mpg...I didn't think it would be that much of an impact.

I think that bolded bit may also be quite relevant. I've seen surprisingly good mpg on journeys where I've seemed to spend ages hardly moving at all.

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There are far too many variables to simply label the A/C as being responsible.

 

As mentioned, uphill vs. downhill, wind speed and direction, fuel variability, ambient temperatures, wet roads, traffic levels, number of stop / starts, the car being dirtier, road surfaces, the list is endless

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I have just done a trip from York to Cardiff, I do the same every year and mine always does better coming back than going.. never turn the AC off.. still got 55 MPG today on the way back... maybe 50-51 on the way down... 

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As above, far too many variable to blame the air con.

 

I've had plenty of long journeys where more congested run with more events of acceleration has returned the better average MPG figure vs a clear run with the cruise on. I blamed the CC for ruining the MPG and even at a safe distance I think the slip stream effect does make a positive difference when the motorway is busy.

 

With modern air con set-ups now it doesn't noticeably affect my mpg at all, i'm still getting better mpg than I was in winter when the air con wasn't in constant use.

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Anywhere towards Wales is most of the time invariably going against a head wind which can be quite strong and therefore have quite an impact on mpg. I have been living in Wales since the 70's with family in Kent, Surrey, Sussex and West Scotland and have experienced the difference in mpg (and top speed with the powerful cars of the 70's) a lot of times especially over the winter periods.

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I have just been to South Wales for a week visiting family, on the way down (220miles) we had a really good run, almost no traffic but used the air con for the whole journey and only managed 56mpg. We came back today, a lot more stop/start traffic jams etc but no air con and managed 66mpg! A massive hit of 10mpg...I didn't think it would be that much of an impact.

 

"Only managed 56" - in my dreams - oh well the joys of petrol - best tank full I've ever had was 53mpg on my Superb II (pre Spritmonitor)

 

On my Superb I 1.9 pd the climate control seemed to make little difference to my economy but on the Superb II 1.4tsi the air con does seem to make a bigger difference but not by 10mpg. It's hard to compare with different journey types - sometimes slow traffic helps the economy

Edited by bigjohn
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Use climate control if you have it as that switches ac off and on as and when

 

I thought most climate control systems cooled (compressor on)  the air and add back in hot air to control the temperature. On my Superb I you had to select "econ" mode to turn off the compressor.

 

I'm not sure how newer systems work when using clutchless compressors but multizone systems have to cope with multiple temperatures 

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My entirely unscientific findings:-

 

Friday: 150 miles Notts to Ipswich - no aircon (not necessary), cruise control whenever possible (70mph), light tailwind, full boot ....... indicated 68.3 mpg;

Sunday: 150 mile return trip - climate ON (22 degrees inside - 25 degrees outside), cruise as above, light headwind, full boot ..... indicated 62.5 mpg.

 

Make of that what you will.

 

Dave

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I thought most climate control systems cooled (compressor on)  the air and add back in hot air to control the temperature. On my Superb I you had to select "econ" mode to turn off the compressor.

 

I'm not sure how newer systems work when using clutchless compressors but multizone systems have to cope with multiple temperatures 

Generally, the climate control system will supply chilled air to the cabin that is then reheated on a zone by zone basis to meet the demands of the cabin via the temperature sensor and the sunlight load sensor(s).

 

Also, the compressor can and does alter the amount of refrigeration work it does. This alters the evaporator's air off temperature to reduce the amount of reheating necessary to achieve the cabin or zone set point. 

 

It's much easier to modulate the reheat quantity than it is to control refrigeration quantity across dual, tri or quad zone systems, especially as cars are still using relatively old fashioned thermal expansion valves on a common evaporator coil, rather than more precise pulsed electronic versions. 

 

Modern car compressors aren't on/off jobbies any more. This allows for more efficient operation, as A/C compressors - as we all know - are big energy hogs. Also, the compressor never switches off entirely (runs at around 2% duty IIRC). This ensures the drive shaft seal remains lubricated to prevent or reduce leakage of R134a. A dry shaft seal is the most common cause of refrigerant loss.

 

My car has an Eco setting that backs off the amount of work the compressor can do, despite cabin demands. I'm not sure what the exact figure is, but 50% would make sense. 

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Modern car compressors aren't on/off jobbies any more. This allows for more efficient operation, as A/C compressors - as we all know - are big energy hogs. Also, the compressor never switches off entirely (runs at around 2% duty IIRC). This ensures the drive shaft seal remains lubricated to prevent or reduce leakage of R134a. A dry shaft seal is the most common cause of refrigerant loss.

 

 

 

Great description thanks,

 

My Superb II has manual aircon with a clutchless compressor (unlike my previous Superb I). Does the the compressor fully turn off when air con turned off?

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Obviously the Ambient Temp makes a difference, not only to the engines efficiency but to CC / AC.

 

Bring a cars interior to 18*oC when outside is 22*oC is lots easier on Energy use than an outside 28*oC & interior starting at high 30's *oC, 

 

So lots of A/C's will be going on today and tomorrow regardless of the MPG it costs if any,

or get the top down, open or get the windows open.

 

Lots of Owners Manuals are for World Wide Regions, read a KIA manual or the likes and the humidity and temps they are talking about are not really as experienced in the UK that often if ever.

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Air con can consume some fuel for sure but there might be different reasons there too.

 

I often do ~200 km trips on the same route with my 2,0 TDI Octavia. I watch the average fuel consumption shown my computer (of course, it's always higher in real life but it shows the idea - is it more/less this time compared to yesterday or next week).

Usually it is from 3,7 l/100km [64 mpg] (rarely) to 4,7 l/100km [50 mpg] (not that often too). Usually it's somewhere in the middle. I have tried to see what affects the fuel consumption but I wasn't able to make any connections between fuel consumption and different factors - weight, speed etc..

Sometimes with full car, driving fast (overtakings etc.) it shows less then 4 l/100km but sometimes in good driving conditions it is no less than 4,5 l/100 km. By the way, there was quite hot outside like a month ago. I drove home when it was 32-34 degrees outside and my air con worked rather hard. Fuel consumption was like ~4,3 l/100km - no more than average.

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