Vacuum noise when turning car AC on.
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?
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
Yes they are vacuum controlled on yours and there is probably a small leak in the lines under the dash or in a actuator.
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.
I also think it is a vacuum leak possibly in the A/C control unit on the dash.
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.
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