Air con or econ?

Does it actually make any difference to the MPG on a TD5? Hubby likes to follow the book and switch the econ on when the temp outside is lower blah blah but then Dexter steams up if its raining so I keep air con on.

Now then what do you think ??

Air con increases electrical load on the alternator, and hence does worsen MPG, also seems to dry me out on long journeys (dry throat, but maybe it's phychosomatic).
To answer your question, here's a quote from the National Renewable Energy Laboratory:

"The power necessary to operate a vehicle air-conditioning compressor is significant, it can be greater than the engine power required to move a mid-sized vehicle at a constant speed of 56 km/h (35 mph). A 400-W load on a conventional engine can decrease the fuel economy by about 0.4 km/L (1 mpg)."

I think running the aircon makes sod all difference if you're going to open a window instead of running it. And given the Disco has the aerodynamics of a barn the additional horsepower drain probably isn't very noticable. But you're a lucky sod anyway, mine doesn't have aircon!

it will worsen the mpg but no more than opening the window
you should use the air con at least once every two weeks otherwise the seals dry out and the compressor will fail which cost about £700 to replace

I like these questions i actually know the answer to something on here

simon holland said:

it will worsen the mpg but no more than opening the window
you should use the air con at least once every two weeks otherwise the seals dry out and the compressor will fail which cost about £700 to replace

I like these questions i actually know the answer to something on here

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Cept for the cost does the seals dyin out with lack of use apply to all aircon units regardless of vehicule??

yes it does, i would tell why but it a bit complicated and only fellow air conditioning and refrigeration engineers would understand

Thanks Simon. Just goes to show you live and learn.

simon holland said:

it will worsen the mpg but no more than opening the window
you should use the air con at least once every two weeks otherwise the seals dry out and the compressor will fail which cost about £700 to replace

I like these questions i actually know the answer to something on here

Click to expand...

I would have to second that, but I would imagine that it could be run for a short period, and of course you dont have to have the windows right down, just a tad to vent, or the sun roof tilted a bit.

This was tested on mythbusters.

OK wow thank you very much ..... and Gaviatrix would never be without air con, it great for keeping kids dogs and the shopping cool!!!!

Seriously thanks for that, the answer is I guess to follow the handbook. So one nil to hubby then?

Air con is a must here in Spain but another 'must' is regular use as already advised, also if you use the 'recirculate' setting for too long then condensation builds up in the car furnishings. This can lead to nasty smells after awhile, use the recirculate setting as little as possible.

Incidentaly, if you have a 'smelly' car then you can buy a can of 'stuff' (technical term) that is opened like a can coke and put on the floor in the car. All windows are shut and the air con is put on recirculate (how ironic) which then using an anti bacterial 'mist' kills the bacteria in the furnishings and giving the car a nice smell.

NOTE!!!!! No you do not sit in the car with this stuff going around and around!

NO NOT ME, a friend, and his throat was as rough as a bears a*se for a week!

regards

Dave

LOL Dave thank you. Not a smelly Dexter yet, only use recirc if they have been muck spreading in these parts teehee!!!!
Thanks again
Dexter's Mummy

Both my discos have air con. The 300 tdi is 14 years old and i use it once a week and have never had a problem except it does hammer fuel consumtion.

The td5 I ude it once a week but can tell no difference on the fuel front as it is so bad anyway! Stinking auto thing.

I have started using the air con on my TD5 now that its been sorted (burst pipe) and to be honest can't see any difference in the MPG - I travel on average 1000miles a month. Also I use it all the time in the company cars as I don't have to pay for fuel and you can go fast again coz you don't pay for fuel.

I jsut cannot see the difference in the fuel costs as Pindie says the M{G is crap anyways!

I always enjoy people moaning about how crap their aircon is at cooling the car down when they have recirculate off or a window open. It will take forever if you're trying to cool down the whole ****ing earth!!!

I'm still a bit miffed at the fact that your car has a name *smirk*

To be honest, I really don't think you will see a difference in MPG. If there is one, it's almost certainly negligible.

Hmmm, I rarely use it, I prefer to crack the window open a bit.....

As for MPG, **** knows, but I do know I can get 260 miles to 71 litres of LPG

TD5s are so bad anyway, 5-10% extra to stay cool isnt too bad. Its not like they do 70MPG without and 60mpg with it on. Its probably like 1-2Mpg differnce, and as most peoples driving is a mixture of urban and extra urban, it will just get lost in the average. 20Mpg around town, Love it!!! NOT

Using the air con does reduce KPL on my car and it is noticable.

But try this on any air con car. Steady speed perhaps 50 KPH, flat road, and note the speedometer reading. Now switch on the air con to see if you can 'feel' it engage.

Possibly because my car is old and the air con system design is out of date but if I switch on the air con whilst in this 'steady state' driving my car feels as though it has run into an oncoming wind. It can be felt as the car slows slightly by 2 maybe 3 KPH. To regain this speed I have to press the throttle down a little to bring the speed back up.

At idle, if I switch on the A/C the engine speed falls, on more modern cars there is normaly some form of idle correction to keep the speed constant.

Petrol engines in the past had a small solenoid that opened to the air allowing the idle speed to increase. Or perhaps advance the ignition a little to cater for the power loss. Modern diesels can change the timing to compensate. On old diesels (such as mine) there is no such gadget. I honestly do use more fuel when A/C is on.

The load on the alternator increases with power requirements, for example with nothing else switched on flick on the main beam and the load on the engine increase as the alternator responds now think of the load applied when the A/C is switched on. Compressor clutch, outside fan, inside fan ect, now add that to the load the compressor itself applies to the engine.

If you are driving an accessory then it needs power (even if it's a small amount) and power (in this scenario) = consumption of fuel, it's a fact of life.


regards

Dave

TheVengefulElephant said:

I always enjoy people moaning about how crap their aircon is at cooling the car down when they have recirculate off or a window open. It will take forever if you're trying to cool down the whole ****ing earth!!!

I'm still a bit miffed at the fact that your car has a name *smirk*

To be honest, I really don't think you will see a difference in MPG. If there is one, it's almost certainly negligible.

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All my cars have had names .... msot being co cars too!! Worked for a few car manufacturers! Oh and Dexter has a girlfriends, Marth the Marvellous Multipla ................ blinking brilliant she is.

Dave - its not accessory and no it has little difference on the idling speed of Dex.

So I think I win this round don't you think?

Well I'll let yu off