# Auto Heat Question



## drbmw (Oct 12, 2003)

When you choose the "auto" button for heating/cooling control, I notice that the air conditioning button automatically comes on, even if you're driving in winter conditions. I understand that the air conditioning keeps the air in the cabin from being too humid and fogging up the windshield. My question is, does having the air conditioning on all the time like that cause the air conditioning compressor to be on and subsequently 1) rob power from the engine and 2) decrease gase mileage? It's easy to turn the air conditioning off, but if it doesn't matter that if affects power or mileage, why bother. Just wondering.


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## ibew595 (Jan 18, 2004)

drbmw said:


> When you choose the "auto" button for heating/cooling control, I notice that the air conditioning button automatically comes on, even if you're driving in winter conditions. I understand that the air conditioning keeps the air in the cabin from being too humid and fogging up the windshield. My question is, does having the air conditioning on all the time like that cause the air conditioning compressor to be on and subsequently 1) rob power from the engine and 2) decrease gase mileage? It's easy to turn the air conditioning off, but if it doesn't matter that if affects power or mileage, why bother. Just wondering.


 :dunno: As far as I can see, yes it would decrease power and fuel economy. It would not be that much at all, but it would exist. Since you are able to selectively control the temperature in the passenger and drivers areas you would need the AC to control temp. Otherwise all you would be doing is mixing ambient air with hot air. Which is ok during winter but not summer. It does remove the moisture so the interior doesn't fog up.
Oh well, what was the question? ramble, ramble, ramble.........


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## drbmw (Oct 12, 2003)

ibew595 said:


> :dunno: As far as I can see, yes it would decrease power and fuel economy. It would not be that much at all, but it would exist. Since you are able to selectively control the temperature in the passenger and drivers areas you would need the AC to control temp. Otherwise all you would be doing is mixing ambient air with hot air. Which is ok during winter but not summer. It does remove the moisture so the interior doesn't fog up.
> Oh well, what was the question? ramble, ramble, ramble.........


Thanks. That's what I thought too. I figure during winter conditions in Wisconsin, there is no reason to keep the air conditioning on, since neither I nor the passenger would turn the thermostat down far enough for the AC to kick in. We're just trying to stay warm here in the Northland.


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