Dave Looman
Ansys Employee

The SF command is a "convenience label" that allows you to specify convection on element faces based on whether their nodes are selected.  Internally, the convection boundary condition is converted to an element load, SFE.  To delete the convections you need to use SFEDELE, not SFDELE.  I found through testing that you can only apply convections to a surface if the overlaying elements are unselected.  You must be doing that.