Mindful of the recommendations to give the aircon a run even in the winter I pushed the button today. It got me wondering (as I was doing 70mph) - is it kinder to the system to switch it on at tickover - or even before starting the car ? After all, it is a clutch. I suppose I am being a bit anal - but what is the view?
I just leave it on all the time.
The clutch cycles the compressor on and off when running anyway.
I would have thought that it would be easier on the engine and starting system to leave it off until the engine is running. But it might be delayed by the ECU or other controls anyway, I don't know. Mine ran out of refrigerant years ago, so it doesn't matter.
I think it's normally an electromagnetic "clutch": the switch turns on an electromagnet on the engine plate of the clutch which attracts the air-con compressor plate, so there's probably no actual friction between pads and plate as the drive is taken up. Still maybe marginally kinder to turn it on before starting the engine.
There is a good group for cars - uk.rec.cars.maintenance . It's a bit quiet, but the specialist advice available is excellent.
DerbyBorn presented the following explanation :
Mine defaults to enabled all of the time anyway, a climate system. The compressor clutch will be constantly engaging and disengaging - so it is designed for that. In winter it dries the moisture from the air flow too, so I just leave it to look after itself.
The old advice was to run it regularly anyway, to help keep the seals lubricated, but I understand that is no longer the case.
Fine, but I always thought that is=t had big impact on fuel efficiency.
I tend to use mine as and when it is necessary, and turn it off (for fuel efficiency reasons) when it's not needed. I use it in winter to dry the air that is demisting the screen, but I turn it off once it's done the job because my car heater doesn't get hot enough to overcome the cooling of the aircon, so the air that's trying to keep the car warm never gets hotter than tepid with it on.
I hadn't realised that the clutch was constantly being cycled on a thermostat when it's on: I assumed that the compressor was permanently on when the button was pressed which is why the air gets so damn cold. Maybe it's only cycled if you have climate control.
hardly a huge issue at any speed
Aircon pump aint much of a load - less than 5bhp Id say
Except that I am fairly sure its wont actually activate until the engine is running these days
Well obviously it takes power top drive it. Its more a question of how much..
..and some studies concluded that having te window open instead, caused more loss of fuel efficiency ;-)
Quick google - 5-10% if one can believe what they find on the 'net.
Just leave it on all the time. It's most useful in miserable damp weather in the UK, anyway, because it's quite simply the quickest and best way to keep all the windows clear.
Remember, it's not just cooled air (which can be heated), but DRIED air.
The compressor is switched in and out regularly whilst the aircon's running. I really wouldn't sweat it.
Many of the people there are here, too.
Not significantly.
Is your thermostat knackered? Getting warm, dry air should be a doddle.
I simpy leave mine switched on - all the time. It stops the car misting up when its cold outside.
I think it's more or less certain that having the windows open causes more losses due to turbulence and "blowing across the neck of a bottle" effect than using aircon to keep the car cool.
Well without aircon turned on, and with heater temp set to hot, the air coming from the heater is very hot, so maybe the aircon has too much chilling effect. With no heater (temp on cold), the aircon quickly produces condensation on the outside of the screen where moisture from the air outside condenses!
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