# My car sounds like truck brakes when I turn on the A/C
**URL:** https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764
**Category:** Factual Questions
**Created:** [June 26, 2018, 12:55pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764 "2018-06-26T12:55:24Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@DummyGladHands](https://boards.straightdope.com/u/DummyGladHands)
#### Post date: [June 26, 2018, 12:55pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/1 "2018-06-26T12:55:24Z")
Just that. I start the car, all normal. I turn on the A/C and whoosh, from the front end, driver’s side, there is a quick outrush of air that sounds like truck brakes.
2007 Grand Marquis, with about 135000 miles. Any ideas? Am I losing Freon?
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### Author:  [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)
#### Post date: [June 26, 2018, 1:01pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/2 "2018-06-26T13:01:08Z")
Your a/c condenser cooling fan is kicking on is what it sounds like
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### Author:  [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)
#### Post date: [June 26, 2018, 1:03pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/3 "2018-06-26T13:03:46Z")
Is it instantaneous? Or does it take several seconds to come on? If freon came out like that it would quickly be empty. i would check and see if any of your under the hood cowlings are missing or loose, it sounds like something where the sound has just changed to something you are not used to.
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### Author:  [@Khendrask](https://boards.straightdope.com/u/Khendrask)
#### Post date: [June 26, 2018, 1:23pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/4 "2018-06-26T13:23:02Z")
Is this MAX AC (recirculate) or AC with Fresh air intake?
It sounds to me like the internal re-circulation damper is switching position.
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### Author:  [@DummyGladHands](https://boards.straightdope.com/u/DummyGladHands)
#### Post date: [June 26, 2018, 1:45pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/5 "2018-06-26T13:45:23Z")
Pretty quickly. maybe 2 sec. and I have never heard this previously. Not Max A/C, just normal . Guy at Auto Zone mumbled something that sounded like “it’s your door left open.”
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### Author:  [@beowulff](https://boards.straightdope.com/u/beowulff)
#### Post date: [June 26, 2018, 1:55pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/6 "2018-06-26T13:55:21Z")
Sounds like a vacuum motor failing.
You need to start searching for the various door controls in the AC system - the blend door, recirc door, etc.
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### Author:  [@awldune](https://boards.straightdope.com/u/awldune)
#### Post date: [June 26, 2018, 4:41pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/7 "2018-06-26T16:41:21Z")
Does the AC still work? Does the noise continue indefinitely or does it stop after a little bit and then come back?
I had a car that would make a whooshing or perhaps a sucking sound whenever the AC compressor came on. This sound would go away after a few seconds. The AC worked OK, but I had to add more refrigerant every summer due to a slow leak. It kept this up for 14 years until I sold the car. I always figured the sound was related to air in the system.
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### Author:  [@cornflakes](https://boards.straightdope.com/u/cornflakes)
#### Post date: [June 26, 2018, 5:44pm UTC](https://boards.straightdope.com/t/my-car-sounds-like-truck-brakes-when-i-turn-on-the-a-c/816764/8 "2018-06-26T17:44:56Z")
AC only, or does it do it when you use the vent or heater functions without AC? 11 years is old enough that the bushings for the blower motor might be dry. Really, it may be a matter of figuring out what might make a sound like that.