I'm new to air con. General advice?

reeac

sheramber wrote: »

But i the computer was 10% out it would be 10% out on both with and without AC.

One time I checked without air con on the journey to a place, then on the way home with air con I used less fuel on the way back.

I once had the same experience doing a particular 150 mile journey a number of times. Traffic density had a bigger effect than anything else....denser traffic meant slower driving and more mpg. That was in a Jag xj6 4.0 manual.

EdGasketTheSecond

sheramber wrote: »

But i the computer was 10% out it would be 10% out on both with and without AC.

One time I checked without air con on the journey to a place, then on the way home with air con I used less fuel on the way back.

Your engine was warmed up already for the return journey. Air con definitely will use petrol as the compressor is driven by the engine and presents a greater load when in use than when disabled. There's no such thing as a free chill!

neilmcl

EdGasketTheSecond wrote: »

Your engine was warmed up already for the return journey. Air con definitely will use petrol as the compressor is driven by the engine and presents a greater load when in use than when disabled. There's no such thing as a free chill!

No, most modern ac compressors are electrically driven rather than directly off the engine. That's not to say there isn't some trade off but it isn't as great as some people imagine.

reeac

neilmcl wrote: »

No, most modern ac compressors are electrically driven rather than directly off the engine. That's not to say there isn't some trade off but it isn't as great as some people imagine.

I'd be surprised if that were the case. Just 1 bhp for the compressor would require over 60 amps draw on the alternator output. You may be being confused by the compressor being driven via an electrically operated clutch.

IamNotAllowedToUseMyName

neilmcl wrote: »

No, most modern ac compressors are electrically driven rather than directly off the engine. That's not to say there isn't some trade off but it isn't as great as some people imagine.

There is plenty of evidence to show that driving with the windows down even a small amount causes at least as much loss of fuel economy as air con. Like a fridge, the compressor is not running continuously.

I do find it amusing that people will pay the second largest amount of money in their lives for a car (several times in their lives) and yet will worry about a tiny proportion of that cost and be uncomfortable. If the cost of running a/c is make or break, then don't even think about depreciation!

scd3scd4

Made me think. We have a second car. Nissan Micra 10 years old about 38k and never had the air con recharged on it but still works fine.

Strider590

IanMSpencer wrote: »

There is plenty of evidence to show that driving with the windows down even a small amount causes at least as much loss of fuel economy as air con. Like a fridge, the compressor is not running continuously.

I do find it amusing that people will pay the second largest amount of money in their lives for a car (several times in their lives) and yet will worry about a tiny proportion of that cost and be uncomfortable. If the cost of running a/c is make or break, then don't even think about depreciation!

That is not all that common any more (although it very much used to be), lease/pcp is more common now, in which case the individual is paying the equivalent of a small mortgage every month. Most people buying this way will buy the most expensive car they can afford the payments on and in those cases they usually end up with very little spare cash for fuel and maintenance. Hence the concern over using AC, hence why so many 3 year old cars run on £20 a corner ditch finder XLs, hence why you see these big expensive cars at fuel stations with the owner topping up £5 a time.

If credit was not a thing and people bought what they coulkd afford, then nobody would really care about the cost of runniing their AC, tax, maintenance, etc etc etc.

Gloomendoom

neilmcl wrote: »

No, most modern ac compressors are electrically driven rather than directly off the engine. That's not to say there isn't some trade off but it isn't as great as some people imagine.

As far as I am aware, electrically driven a/c compressors are not normally fitted to IC engined production cars.

JohnB47

Great thread. Thanks for all the info.

As with many things, there are different views. I particularly like the post by IanMSpencer, although others have made similar points.

I've been driving for a few days with Climate Control on - (Honda Jazz 1.3 EX). When stationary I can hear a fan coming on and off, fairly regularly. About 5 seconds on, 30 seconds off. While the fan was running, I switched the CC off and the fan stopped. So it's the CC rather than the rad fan.

I'm also noticing a sort of hesitancy in the car with CC on. Sometimes it feels like I've lost a bit of power and sometimes I feel a small boost of power, like someone has just pushed gently on the back.

Is this the CC using draining a bit of power or am I imagining it?

Presumably this is all normal stuff, that I need to get used to?

scd3scd4

Use to work with a fitter who was on good money. Purchased a new Jag but was always complaining how expensive the AC was!!!