Having problems with your 2003 Chevrolet Impala ?
Rear defroster stop working and horn - 2003 Chevrolet Impala
On this year vehicle the flapper should be vacuum controlled. You may want to look at the vacuum lines\015\012 \015\012going to and from the vacuum canister in the engine compartment. If it will change from floor to dash but not defrost\015\012 \015\012then you may have a failed vacuum line or diaphragm in the dash from the selector.
Repair Help & Product Troubleshooting for 2003 Chevrolet Impala
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