Vacuum noise when turning car AC on.


Asked by May 30, 2013 at 08:10 PM about the 2007 Mercury Grand Marquis LS Premium

Question type: Maintenance & Repair

My car AC works fine but ive noticed when the AC is turned on I hear a steady vacuum
noise that comes on. Its pretty noticeable and fairly loud. When I turn the ac off I still
hear the noise until I turn the car off. If I don't use the ac I don't hear the noise at all. I
see no leaks from the vehicle. Any suggestions what could be causing this?

5 Answers


Some of the heater/ac controls are vacuum operated. I'm not sure if they are on your car but this could be a starting place. Good luck, J

2 people found this helpful.

Yes they are vacuum controlled on yours and there is probably a small leak in the lines under the dash or in a actuator.

2 people found this helpful.

The sound you hear could be the cooling fans kicking on. When the A/C compresser starts, strain is put on the engine and it heats up. The rad. fans kick on to keep everything cool. They will often continue to run until the key is off.

1 people found this helpful.

I also think it is a vacuum leak possibly in the A/C control unit on the dash.

1 people found this helpful.

Check on the bottom of the steering column there is a vacuum controlled switch that releases the parking brake when you put it in drive (even though it has a manual release) I would start there thats where my leak was and I myself didn't know it had one you didn't state what year your car was my is a 1987 Mercury Grand Marquis.

3 people found this helpful.

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