I have a 2001 4.6 and when I turn my heat on to floor or any other setting except defrost the defrost kicks in and out. Is that normal also when on defrost just the defrost works which is normal.

 

You likely have a vacuum leak in the lines that supply the vacuum motors that control the flow of air in the dash.

The system is designed to default airflow to DEFROST outlet in the event that vacuum is lost. This is to ensure that you at least have a clear winshield for safety.

Track down the vacuum line from the intake manifold and inspect if for leaks up to where it passes through the firewall. If no leak is found there, you will have to start looking inside the dash for the vacuum loss.

Steve

 

look behind the battery