I was told in my 04 5.4l expedition I could not bypass ac because defrost is linked to it is this true. If not were can I find bypass pulley or just us one for an 03 5.4?

 

A/C when in defrost or mix mode serves to dehumidify incoming air hitting the windshield and glass---without the compressor engaged that doesn't happen.

It should be okay to re-route the drive belt away from the A/C compressor, control of the duct air flow not affected or disabled by that action.