Q: my a/c blows out the defrost nomatter what mode its in on 2003 Chevrolet Silverado 1500 HD

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no check engien light is on .i did just put a k&n air cool filter
(1) Answer
This is the default for when there is a problem with your A/C system . It is a safety state so you will have a defrosted windshield and usually there is heat in the defrost air as well.

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