Compressor runs with heat on

I own a 1999 Ford F150 V 8 5.4 L . I have recently notice that my A/C compressor clutch will engauge when the heat is on. A mech. told me that the compresssor should run to get out the moister and that this was normal. Many friends have the same truck but a year or two newer. thier trucks do not do the same thing. I have been told also that it is the clutch hanging up, and should replace the compressor and clutch. Has anyone else ever had this problem or seen it be for. Any help would be greatful.

The A/C should ONLY cycle in a defrost mode (defrost or heat/defrost). If it's on at any other time, it is not right.

If the clutch is dragging, you'll hear a scraping noise, but it will NOT turn the compressor "at speed".

Dont worry, it's 100% normal. It also keeps them from seizing up. Worry no more.