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Q: the ac only works on defrost

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When I try to turn the A/C on it will only blow out through defrost

My car has 150000 miles.
My car has an automatic transmission.

Air is directed between the different vents by vacuum. When the a/c controls are moved to the different positions, this signals the blend door, or doors, behind the dash to redirect the airflow. A few things can keep that from happening. Broken or maladjusted cables to the blend door, broken or detached vacuum lines, or a broken/stuck blend door. There should be a vacuum supply line from the engine that typically will run through the passenger side of the firewall under hood. make sure that line is connected and has a good vacuum supply. If that line is good, then further diagnosis under the dash and of the a/c controls are in order. Have a certified technician look into the dash air flow issue if the vacuum supply is good.

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