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Q: Ac & heat only blow out of defroster when I turn the

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When I turn the heat or Ac on, no matter which setting I choose it only blows out of the defroster, won't blow out of vents or floor

My car has 203000 miles.
My car has a manual transmission.

A: It sounds like you have a problem with the ...

It sounds like you have a problem with the vacuum supply to the HVAC control head. Engine vacuum is what changes the airflow to the vents and floor. Defrost is the default position when there is not a vacuum source.

  • The first place to look is under the hood. Look for any vacuum lines off or damaged around the intake manifold.

  • Next, check the vacuum reservoir above the splash shield in the RF fender (plastic tank). Check for cracks or broken nipples. (If you have 4WD, this also supplies vacuum to engage the hubs and transfer case. If the there is a leak in that system, the HVAC will be affected.) From the plastic tank, a vacuum line runs to and through the firewall into the dash.

It’s possible the you have a leak behind the dash, or a bad control head, but a problem under the hood is more likely. If you need assistance in locating the problem, consider YourMechanic. A mobile mechanic can diagnose the issue with your AC system at your home or office.

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