# Variable Volume A/C compressors

**URL:** <https://boards.straightdope.com/t/variable-volume-a-c-compressors/555790>\
**Category:** Cecil's Columns/Staff Reports\
**Created:** [October 1, 2010, 11:31pm UTC](https://boards.straightdope.com/t/variable-volume-a-c-compressors/555790 "2010-10-01T23:31:33Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![epotter](https://avatars.discourse-cdn.com/v4/letter/e/f19dbf/32.png) [@epotter](https://boards.straightdope.com/u/epotter)\
**Post date:** [October 1, 2010, 11:31pm UTC](https://boards.straightdope.com/t/variable-volume-a-c-compressors/555790/1 "2010-10-01T23:31:33Z")

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So in today’s post about auto A/C (with it’s interesting, if sadly unsurprising result) you missed a part of the A/C question that I would have liked to see answered.

The poster was from Tuscon, so in terms of relevance to him/her/it having the A/C running full blast seems appropriate. But for those in more moderate climates, I would wonder how variable-volume A/C compressors change the equation. The idea (or so I gather) about them is this: if you only need to cool the air inside the car a few degrees, you need less oomph from the A/C compressor than you would if you need to cool it by 20+ degrees, so it reforms itself to use less than its maximum capacity rather than running full blast for a while, switching off for a while, running full blast for a while longer, etc. In the owner’s manual for my 1993 Audi, one of the selling points for this was more efficient operation (it had a little tree next to it and everything - the tree signifying how much Audi cared about the environment. Eh).

I live in Houston, which is as close to hell as it gets, so I’m not sure I could provide any helpful real-life data about A/C operation in moderate temperatures. But I would be interested to know if in general, the idea is sound, or if it’s just car manufacturer malarkey.

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**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\
**Post date:** [October 2, 2010, 12:23am UTC](https://boards.straightdope.com/t/variable-volume-a-c-compressors/555790/2 "2010-10-02T00:23:30Z")

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Welcome to the Straight Dope Message Boards, **epotter** , we’re glad to have you with us.

When starting a thread, it’s helpful to other readers to provide a link to the column in question. It’s on the front page now, but in a few days it moves down the list. So, here’s the link: [Has auto AC been improved so much it’s no longer an energy sink? - The Straight Dope](http://www.straightdope.com/columns/read/2961/has-auto-ac-been-improved-so-much-it-s-no-longer-an-energy-sink)

Also, there’s already another thread on this topic. I’m going to close this one, and suggest folks go there: [AC on/off Corvette at 55 mph data right? - Cecil's Columns/Staff Reports - Straight Dope Message Board](http://boards.straightdope.com/sdmb/showthread.php?t=580348)

**epotter** , if you’d like to repost in that thread, that’s OK. Or if you’d like me to merge your post into that thread, I’m happy to do that, just email me.