Climate Control

[edcs]

Haven't had automatic climate control before, so a bit of a n00b question; But on a 986 Boxster (or any other car I guess), if you have the climate control set to automatic the AC symbol is illuminated. Does this mean that the AC is actually turned on and dehumidifying the air going into the car? Only ask as someone mentioned it to me and if this is the case do you save a little fuel turning it off?

[TonyB66]

Yes correct on both questions. If you have it on the engine will idle with a few more revs as the compressor will be running. Just hit the snowflake button at idle and you will hear/feel/see the difference.

[RiccardoG]

Yes, that's correct (auto = ac on) and yes, switching it off should save some fuel. Don't forget to run it about 10min a week to keep the seals lubed and everything working correctly.

[edcs]

Thanks for the advice - guess that's why it's so good at clearing the windscreen then!

[Rockster]

edcs said:

Haven't had automatic climate control before, so a bit of a n00b question; But on a 986 Boxster (or any other car I guess), if you have the climate control set to automatic the AC symbol is illuminated. Does this mean that the AC is actually turned on and dehumidifying the air going into the car? Only ask as someone mentioned it to me and if this is the case do you save a little fuel turning it off?

Unless the outside air temp is below 32F (some sources list this as 34F) the snow flake symbol means the A/C compressor is on.

The auto climate system is a fine system. I've got one in both my 02 Boxster and 03 Turbo.

While the compressor does represent a bit of a parasitic drag it is really insignificant once the cabin temp has been brought to within the target temp.

This is accomplished by the fact the compressor is a variable displacement unit so once the cabin is comfortable the compressor displacement is reduced so just enough cooling is generated.

I have watched the engine load at idle with the compressor off then on and unless the cabin is real hot the load number barely moves.

IOWs, off the engine load at hot idle is 2%. (It could of course be a fraction above this but the differences are the same.) When switched the load increases to not even 3%.

Given my Boxster has a rated output of 220hp this times 2% equals 4.4HP at idle. 220hp times 2.5 is 5.5HP at idle. Big deal. When the engine is running and the car is not moving fuel mpg is 0. Get moving!

Say it costs 1hp but this is not all on the compressor. The cabin air fan motor represents some of that load as do the radiator fans. These are switched on to low speed whenever the A/C is on regardless of coolant temp.

Even with the A/C off if you have the cabin vent fan on this costs you mpg.

The radiator fans may not be on if the coolant temp is below 212F. But if you drive slow enough even on mild day these will come on and then go off over and over again.

BTW, it takes roughly 40hp to move the car down the road at a reasonable steady speed. Another 1 or even 2 hp is not going to make any difference in fuel consumption. In fact if you have the A/C off but the windows down the increase in wind resistance may cost you more in fuel than running the A/C.

('course if you have the top down then there is generally no reason to run the A/C. In this case when I used to run with the top down in cooler weather I'd turn on the system but in manual mode and adjust the heater controls for comfort.)

Really make it easy on yourself. If you need A/C either for cooling or heating or demisting just push the Auto button and set the temp to 72F. The cost in fuel is miniscule. Improper tire inflation of which there is a lot this going around can easily cost you 10% fuel economy.

The system is designed to avoid blowing cold air in your face when you first start the car on a cold day with the system on. As the coolant warms up the system adjusts the vents and cabin fan speed to bring the cabin up to temp absent the freezing drafts lesser systems generate.

Another feature I like is if the outside temp is not too cold or too hot you can get a poor man's auto mode by turning off the fan then pushing the temp control button and adjusting the temp to what you want. The system will adjust the vents, route the air like it does with the system in auto mode you just do not have the benefit of de-humidified air or chilled air. But if the outside temp is reasonable the outside air suffices to keep the cabin comfortable.

Anyhow, regular use of the A/C system keeps the system in good repair. My Boxster's system was 11 years old the 19th of this month and it has never been touched.

Oh, a couple of miles away from your final destination for the day or night in humid conditions turning off the compressor and letting the cabin fan continue to run helps dry the system out and prevents mold/mildew from gaining a foothold.

You will still have to change the cabin air filter once in a while.

In short use the auto climate feature when you want to. It is a very good system efficient. And makes the more comfortable. I see no reason to buy a nice car then turn off its creature comforts. Might as well drive a farm tractor then.