ComboBox.Dropdown Method (Access)
You can use the Dropdown method to force the list in the specified combo box to drop down.
For example, you can use this method to cause a combo box listing vendor codes to drop down when the vendor code control receives the focus during data entry.
If the specified combo box control doesn't have the focus, an error occurs. The use of this method is identical to pressing the F4 key when the control has the focus.