How do luxury cars still blow cold air with engine off?

[Friday13th]

I tried Googling this, but non of the results had anything to do with my question. Nowadays we get cars that are capable of blowing cold air into the cabin when parked in scorching heat. They also have air con that work even though the engine gets cut off (like so many luxury cars we have these days) - the driver stops, engine stops running, still air con works. I drive a 10 year old car and with the engine not running, you get hot air blown to the cabin when the air vents are opened/switched on in summer days. I thought that the air con was operated by the engine running?

 

[AchmatK]

No idea how it's done but the aircon in my car has a "rest" button. If I switch the ignition off, and then press the rest button, the aircon will switch on for about 10 minutes. It's not as cold as it is with the ignition on though.

 

[xumwun]

I doubt they would be able to do this for very long.
Possibly the compressor is electrically powered.

 

[Friday13th]

No idea how it's done but the aircon in my car has a "rest" button. If I switch the ignition off, and then press the rest button, the aircon will switch on for about 10 minutes. It's not as cold as it is with the ignition on though.

Fascinating! I had no idea something like this exists. New cars with stop/start systems (not for the ignition - specifically for the engine...not sure what the correct term is) must be using something similar.

I doubt they would be able to do this for very long.
Possibly the compressor is electrically powered.

With the dozens of electric components that they have, that must put a hefty strain on the battery/alternator?

 

[Sinbad]

No idea how it's done but the aircon in my car has a "rest" button. If I switch the ignition off, and then press the rest button, the aircon will switch on for about 10 minutes. It's not as cold as it is with the ignition on though.

The rest button if you have a Merc is actually for keeping the car warm when the engine is off ;-)

 

[AchmatK]

My car has a power saving mode. If I'm listening to the radio for about 30 minutes, it goes into power saving mode and none of the electrical components will work. Only way is to start it up and let the car idle for a few minutes. I think it's too prevent the battery from draining too much and the car not being able to start up again. I don't miss forgetting to switch off the lights on my Tazz in the morning and having to push start it again.

 

[AchmatK]

The rest button if you have a Merc is actually for keeping the car warm when the engine is off ;-)

Don't have a Merc

 

[ponder]

Electricaly driven ac compressor, electricaly driven power steering. It's the way it's done these days.

 

[ShaneE]

I have the rest button (BMW not Merc), and it's also for keeping the car warm when the engine is turned off.

 

[P924]

The aircon is driven by the engine and will stop if the engine is stopped. It requires far too much power to be driven by an electric motor effectively, not to mention added cost and weight and space. Cars with so called rest functions, or those with stop start functions just keep the blower blowing over the evaporator of the aircon, it will remain cool for a. Couple of minutes after the engine switched off. The heater radiator will remain hot for longer when you are heating the cabin, simply because of the high specific heat of the water that fills it.

 

[gfmalan]

With Audi you have 2 options:

1) When using the stop/start system, it will kill the engine when you stop, but keep all the electric stuff running. The compressor does stop, so in a minute or two you will feel the air is still cool, but slowly heating up (compressor not working). The engine cycles between these modes with I think 3 conditions. If the car's interior temp would drop, if the battery gets drained to quickly or below certain voltage, when the car sense that battery gets to weak from all the stop starts, to start the engine again, it will start the engine and keep it running. (sort-off over-riding it self).

2) Audi has this optional Item that you can get your sunroof replaced with solar panels (from +/- 2006), and then it remove the hot air from car standing in the sun.

I'm not an Audi mechanic, but never came across electric compressor in models from the A4 (2001) - Q7 (2012).

 

[Fazda]

I have the rest button (BMW not Merc), and it's also for keeping the car warm when the engine is turned off.

Modern climate control systems will keep a constant temperature via an electrically driven compressor. You should find that your BM will keep the car cool as well - it works on the same system.

 

[Jola]

Yes, most of the new cars have electrically driven compressors.

 

[pezulu]

The REST button in a Mercedes uses residual air in the cabin, recirculating that air for a few minutes.

 

[Rouxenator]

The rest button if you have a Merc is actually for keeping the car warm when the engine is off ;-)

Correct, our pre-facelift 1994 W202 had that, REST was described as using "residual heat" to keep the heater working after the engine was switched off.

 

[Sinbad]

Correct, our pre-facelift 1994 W202 had that, REST was described as using "residual heat" to keep the heater working after the engine was switched off.

Mercs have a small auxiliary water pump... I'm pretty sure it kicks this on to circulate hot water through the heater matrix.

 

[Aghori]

What is this ac you speak of?

 

[Nerfherder]

I have always wanted a solar system that cools the car from pannels on the roof.

Then you leave your car in the sun and come back to a cool car.

 

[ShaneE]

Modern climate control systems will keep a constant temperature via an electrically driven compressor. You should find that your BM will keep the car cool as well - it works on the same system.

That's sounds pretty cool actually, think i'll try that sometime!

 

[Friday13th]

With Audi you have 2 options:

1) When using the stop/start system, it will kill the engine when you stop, but keep all the electric stuff running. The compressor does stop, so in a minute or two you will feel the air is still cool, but slowly heating up (compressor not working). The engine cycles between these modes with I think 3 conditions. If the car's interior temp would drop, if the battery gets drained to quickly or below certain voltage, when the car sense that battery gets to weak from all the stop starts, to start the engine again, it will start the engine and keep it running. (sort-off over-riding it self).

2) Audi has this optional Item that you can get your sunroof replaced with solar panels (from +/- 2006), and then it remove the hot air from car standing in the sun.

I'm not an Audi mechanic, but never came across electric compressor in models from the A4 (2001) - Q7 (2012).

Thanks for the explanation. Having never driven such vehicles, I would not have guessed this.

What is this ac you speak of?

A fridge someone, long time ago, decided to fit in vehicles.