Should you let your AC run for at least 10mins a Week!

Yes. The seals can dry out when it's not used for long periods and 'pickup' when it finally is causing wear to them.

I have another UK made car with AC which runs the compressor when you select demist - as well as making sure it's used during the winter months the AC helps dry out the air.

Yes probably how I lost refrigerant on my old 740i.

but this does not work below ~2.5C

On 14 Feb 2007 02:13:45 -0800, " snipped-for-privacy@gmail.com" waffled on about something:

According to the E36 manual, yes you should.

BTW, aircon is fantastic at clearing misted windows, turn the aircon on and turn the heater up full.

Just don't leave it like that for too long as the air becomes very dry and your eyes will start to water!

Dodgy.

The a/c compressor runs when you set it on defrost, so this means that most a/c compressors run year round. unless it's very cold. If anything you should set your heating system to floor or vent, that way the compressor will shut off and you'll save money on gas.

On Wed, 14 Feb 2007 07:44:19 -0600, "s" waffled on about something:

That would depend on the car. My '94 E36 certainly didn't do that.

Dodgy.

On Wed, 14 Feb 2007 11:53:31 -0600, "s" waffled on about something:

You need to be careful, the original poster didn't give much in the way of information about his car. We don't know how old it is.

To be honest I've never seen a car do that, but then again I haven't played with any BMW under 10 years old either.

I've always manually done the a/c dehumidify trick.

Dodgy.

I certainly don't know about the actions of older BMWs, but all cars designed in the US use the A/C to clear the windshield during cold weather. They have used that technique for well over 30 years now. My first car with a factory equiped A/C was a 1967 Ford, and it definitely used the A/C in that manner.

Jim

My UK E39 with climate control doesn't.

And my US 2001 E46 doesn't do that - you have to either hit the defrost button (which does turn on the a/c), or manually turn on the a/c.

FloydR

The defrost button doesn't turn on the AC on mine - or if it does, the telltale doesn't light. Nor does the idle speed alter.

There is a difference between normal AC and climate control systems. All of the climate control systems in cars I've owned - all the way back to a 1978 Ford - took complete control of all settings, including the AC compressor operation, when set in full auto mode.

As others have said, an often overlooked function of any AC system is a dehumidifier. That function is equally important in house AC systems, as well as cars.

On Wed, 14 Feb 2007 21:04:46 -0500, Dean Dark waffled on about something:

Hmmm, very curious.

Okay, well I think I know why I have never seen it, and "s" has seen it everywhere since the ark. He's in the US, I'm in the UK. Given that American cars tended to have big engines, I guess the manufacturers weren't really bothered about the extra load of the compressor being engaged when you went to demist the car, whereas with a little Euro-box it was deemed the driver should decide if he wants to loose half the engine power!

The '94 E36 I was referring to did have climate control (all be it the early 4 knob flavour, not the digital one that came along later), and the A/C was something extra you decided if you wanted or not, the way it functioned was more of an add-on than an integrated part of the system. I know for sure the A/C didn't come on automatically when I tried to demist the screen because I used to make a point of manually turning it on. If I forgot, it took ages to clear.

Dodgy.

On Wed, 14 Feb 2007 19:19:01 -0600, "s" waffled on about something:

S, I'm not trying to have an argument here, I'm just saying that what you are saying is a broad generalisation, which several of us here can disprove from out own experiences.

To the original poster, press the button every week or two, a/c will help demist the car, and use of it will keep the seals in good shape. Your car may, or may not do this for you already, without knowing the model/age we can't say for sure, so it's safest for us to say press the button.

Dodgy.

Right - I've just done some checks. With a fully warmed up engine, selecting AC on my climate control E39 causes the rev counter to rise before returning to near normal. The engine note also changes slightly as it's now under load. Selecting defrost does no such thing - so on my car at least it's not engaging the compressor.

That's funny, on mine the air con makes idle speed increase a lot and stay there. I've not had it on for long but it goes from (if the tach is linear at that point) ~250rpm to about 750.

The demist button does not appear to run the air con on mine either. Pity really as it sounds like a good idea, to keep it exercised if nothing else.