I'm new to air con. General advice?

EmmyLou30

Owned 4 cars with air con....in summer months when the air con is working hard 10% extra fuel consumption is about right, obviously negligible in the winter.

In answer to the OP if you still haven't managed to wrap your head around AC in winter: think of it like the air coming in, going through the AC unit that removes moisture and then pumps it into your car at whatever temp you've turned the dial to, be that hot in winter or cold in summer. The advantage in summer is that it's muggy outside so removing the moisture makes the car feel much fresher as well as cool, in winter it means no misting up of the inside when you get in with wet clothes from the rain or on a cold day. Think of it as an air drying unit instead :-)

As others have said, regardless of whether you have manual air con or climate control, you can just leave the AC button turned on all year round and just adjust the temp. People I know who insist on turning it off to save a few pennies have had issues with dry seals or leaks etc as the syatem needs to be run. Personally I also would want a bit of air flow through the system rather than breeding bacteria in stagnant pipes for 6 months of the year before blasting it into a confined space!

BeenThroughItAll

Bearing in mind the tiny amount of power consumed by a typical AC compressor in a modern car, 10% difference in fuel usage is incredibly unlikely to be caused by the AC alone.


Modern HVAC is designed to be used with the AC on full-time.

iolanthe07

I'm surprised that posters are saying that their aircon uses 10% more fuel. I have noticed no discernible difference at all, though I accept that logically there must be some increase.

Apodemus

iolanthe07 wrote: »

I'm surprised that posters are saying that their aircon uses 10% more fuel. I have noticed no discernible difference at all, though I accept that logically there must be some increase.

I agree. Logically there must be some effect but it is really difficult to show it on my car. There are so many other variables related to temperature that probably improve efficiency when the weather is warmer.

However, my climate control packed up more than a year ago and is beyond economic repair. Since I make the same road trip each year to the South of France and keep fuel and mileage records of each trip, I am able to compare the most recent “no air-con” trip with the earlier “constant air-con” trips in a climate where there is no doubt that the air con would be working hard. I still can’t point to any difference in fuel consumption between trips!

System

JohnB47 wrote: »

Thanks, but that's not really getting to the nub of my question. If it's winter (say, 9 degrees outside) and I switch the AC on and select a temp of 20 degrees, the AC won't activate - the heater will.

So what I'm asking is, does this count as 'running' the AC? Or would I have to switch AC on and select 'Lo' as a temperature - and suffer a cold interior for 10 minutes?

You misunderstand how aircon works. It doesn't just make things cold, it can also keep things at any temperature. It actually helps reduce things like misty windows in the morning because it "dries" the air.

When you set the temperature to 20C and its 9 outside the AC actually helps keep it at 20C.

A refrigerated lorry trailer is just a box trailer with a big AC unit bolted on the front and that can work from -30C to +30C.

n217970

So, without quoting posts, to answer some of the 10% sceptics - it is a 2005 Volvo S60 D5 (so plenty of power) that spends nearly all its time wafting along at 50-60mph. It regularly returns 55mpg brim to brim on this kind of commute with the AC off, with it on it manages around 50mpg. Given I am an incredibly boring individual I have tested this theory many times and apart from small variances I find the results conclusive.

I presume it has an impact of around 10% as at 50mph the engine has very little load on it and even a "small" amount extra is quite large proportionally. Maybe if I were stop/start 30mph driving it would account for a smaller % but I can only comment on what I have seen.

BeenThroughItAll

n217970 wrote: »

So, without quoting posts, to answer some of the 10% sceptics - it is a 2005 Volvo S60 D5 (so plenty of power) that spends nearly all its time wafting along at 50-60mph. It regularly returns 55mpg brim to brim on this kind of commute with the AC off, with it on it manages around 50mpg. Given I am an incredibly boring individual I have tested this theory many times and apart from small variances I find the results conclusive.

I presume it has an impact of around 10% as at 50mph the engine has very little load on it and even a "small" amount extra is quite large proportionally. Maybe if I were stop/start 30mph driving it would account for a smaller % but I can only comment on what I have seen.

I've had both an S80 and V70 D5, and both of those would happily return 55MPG in mixed use per tank, and the fully working climate control was never switched off from the day I bought the cars until the day I sold them. I doubt very much they'd have done 60+MPG with the climate control turned off.

IamNotAllowedToUseMyName

The demisting of AC is because in cooling the air, it reduces the amount of water it can contain, and when it gets to about 4 degrees C or below and at that temperature it cannot contain any water, so a decent climate control system will not operate the compressor when outside temperatures are below 4 degrees C - it offers nothing. The demisting issue is that when wet air hits the windscreen, the water that was in the air gets removed from the air as it is chilled by the windscreen.

The dry air can then be heated to be sent to the car at the right temp (and it doesn't get wet again as it is heated). The only problem some cars have is that diesels are slow to warm up so they may have secondary systems to warm the car up - burning fuel for example.

Without air-con, you have to wait until the heater has warmed the windscreen sufficiently to stop the air chilling on the windscreen. Most people are particularly useless at adjusting the heating controls and vents to demist the whole car.

With air-con, you might need a bit of demisting in a cold car, usually there is a button to press, but as soon as the windscreen is cleared, press to the automatic mode and leave the car to work out how to mix the air to the right temp.

One thing with climate control, or even more basic air-con with thermostats (my 1999 Merc had thermostats for passenger and driver so could be left alone, could never work out what the climate control upgrade would do, especially at about £600), is that there is no need to fiddle with the temperature to get the car to heat up quickly - I quite often see people stick the temp up to max, when the car will be delivering the maximum amount of heat anyway if it is significantly under temperature.

Modern air-cons are light and efficient (actually, cheaper to fit than sunroofs, which also needed cars to be redesigned to give the extra headroom absorbed by the sunroof, so sunroofs have died a death). On a small car, there will be some additional fuel consumption, but my experience of air-con is that if you embrace it you'll find that you can drive away quicker, you will be warmer and more comfortable (damp air in winter is chilling) and you'll be able to see where you are going.

It can be worth using the re-circulation setting when the car is particularly cold and or damp to allow the system to treat the internal air quicker though some cars have automatic systems for that.

wongataa

JohnB47 wrote: »

This is all very interesting. I thought AC was simply air cooling. But you're saying that, even if I turn it on and have the heater working, the AC is still working? I can't get my head around that.

The answer is yes. AC dries the air. To do this it also cools it (useful on hot days) but you can also use your car's heater to heat this dry air back up until it is warm/hot. The AC and heater are separate things. You can have both on, or either one on and not the other.

On my car I have a AC button and a heater knob. Pressing the AC button has no effect on the heater setting. Adjusting the heater has no effect on the AC on/off state.

Climate control is just a fancy control system where you set the temperature level and the car automatically adjusts the heater & AC settings to maintain the set temperature.

n217970

BeenThroughItAll wrote: »

I've had both an S80 and V70 D5, and both of those would happily return 55MPG in mixed use per tank, and the fully working climate control was never switched off from the day I bought the cars until the day I sold them. I doubt very much they'd have done 60+MPG with the climate control turned off.

Now is that from the computer or actually calculated from fill ups? As I have found the computer to be wildly over optimistic; mine is currently showing 64.2. With the AC on it would be around the 58-59mpg mark. 55mpg on the computer in my car would be around 47mpg calculated.