Q: Problem with AC

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When I accelerate up to 30 MPH (and beyond) my AC switches from blowing forward, to blowing out of the dash like a defroster. Then, when I stop accelerating it switches back. What might be causing this and how much do you think it'll cost to fix?

My car has 40000 miles.
My car has an automatic transmission.

You have a leak in the A/C vacuum system. Look out in the engine compartment near the blower A/C evaporator case for a vacuum line with a small vacuum canister and look for leaks in the hose or canister. The A/C vacuum system operates the A/C blend doors and defaults to defrost mode when vacuum is lost. If you’re interested in having this done, a technician from YourMechanic can come to your home or office to inspect the AC and quote you on any repairs that are necessary,

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