Do you keep the AC on at all times?

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daniel_c

Member
Tonight I was out on a top-down cruise, it was pretty chilly, 15-16C, so I had the heat set to around 24C.

First, the drive was lovely, the heat seems to somehow stay in the cabin despite the top being down, and slowly cruising on chilly nights is my favorite :)

However, it got me thinking about AC. I always have the “AUTO” mode enabled, and I figured that would also automatically toggle the AC depending on need, but as far as I can remember, the AC is pretty much always on.

Tonight, I really wouldn’t have needed it at all, tho I know that AC doesn’t only just chill the air when needed, it also dehumidifies it, and despite being a chilly evening, it is pretty humid.

Since there is no dedicated hardware button for the AC, I just keep it on. Is that a good idea or not? And do you know if the AUTO mode is supposed to enable/disable the AC, or does it basically only control the fan speed?
 
Oh, and a bonus question, when I parked the car for the night, I noticed a liquid dripping from underneath the car. I panicked at first, but then I remembered it’s probably just water from the AC dehumidifying the air.

The liquid had no odor at all, was clear and had no thickness, so I can only assume it was just water. The location of the dripping was pretty much in the middle of the car, I’d say approximately underneath the center console.

Just to help me sleep, please tell me that’s where the water outlet is placed? :S
 
Always leave the ac on. Helps circulate the oil in the refrigeration system which prevents rubber seals from drying out and splitting.
It also helps prevent condensation inside the car.
 
ori said:
Always leave the ac on. Helps circulate the oil in the refrigeration system which prevents rubber seals from drying out and splitting.
It also helps prevent condensation inside the car.
Click to expand...
The above is correct, but it does use around 5% more fuel! :)

Seems a bit of a waste of time having the a/c on with roof down. It will just try to dehumidify the entire planet. :thumbsup:
 
Pondrew said:
ori said:
Always leave the ac on. Helps circulate the oil in the refrigeration system which prevents rubber seals from drying out and splitting.
It also helps prevent condensation inside the car.
Click to expand...
The above is correct, but it does use around 5% more fuel! :)
Click to expand...

Might be closer to 8%. Does depend on speed. Over 50mph it’s better to use ac than an open window.

Might experiment on longer journeys if having the ac off actually improves my fuel economy. Problem is, in hot weather, I have the roof down and that can’t be good for fuel economy. ;)

Plus I also keep the cold air ac on if it’s really hot. ;)
 
Thanks both!

The fuel usage is not a big deal to me (since I really don’t drive a lot) but it does feel wasteful having the AC on while the roof is down.

Do you happen to know what exactly the AUTO mode does?
 
If the car has auto setting you have climate control you should leave it on auto with the roof up, the compressor does not run unless you are actually cooling the air. You may think it is because the pulley is still turning but there is a magnetic clutch to engage the compressor, so you are not using any more fuel at all in cool weather.
Does any model of Z4 disable aircon with the roof down?.

With the top down in hot weather turn aircon off because you are trying to cool the sky, in Spain recently it was so hot we had to put the roof up and use the aircon
 
If it is really hot, I use the aircon to blow cold air at my feet and face when the roof is down so no, it is not disabled for the e85 at least.
 
Yup. On a hot day I keep the aircon on with the roof down so I get some cooler air blowing at me.
Same as having hot air when it’s colder and roof down.

On a rainy day if you turn off the ac you get a condensation inside the car but with the ac on, it stays clear.
 
F1SpaceMonkey said:
Only turn AC on when i need the cabin cold on hot days. 350 days a year AC is off, as is Auto function.
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If you don’t use it regularly there is much higher chance for the system to break. It is recommended to use the AC at least once every month.

Not sure about the G29 but on my E89 I have noticed when you open the roof the air con automatically lowers quite a bit, it doesn’t switch it off entirely but it does drop. Maybe it does the same on the G29?
 
I have A/C on both my BMW,s and most of the time its off, i do switch it on obviously on hot days, or at least once a month to circulate the oils etc.
I dont use it if i have the roof down, on the Z4, a bit pointless really.
Its easier to switch off/on , in my X5 as there is a button to do so, but in the Z4 i have to go into the a/c menu in the idrive and turn it ,, on/off there... :driving: :driving:

And yes the water under the car is from the A/C system...
 
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