Using Access Form Control as SQL Function criteria

I have a combo box named [myControl] on an Access form that I can use to select/enter a site name (ABC).  There is a button on the same form that runs a report.  The underlying record source for the report is a SQL Function.  Is there an easy way to pass the combo box value to the SQL Function so that only records for site 'ABC' are displayed in the report?  I tried Forms![myForm]![myControl] in the criteria box of the Function and it did not work.  THANKS!