Delete other values except "A" and "B" and "C"

Sub replace_but_ABC()
Dim i, str, replace_but_ABC
str = "AAasdvjVBC"
For i = 1 To Len(str)
    If Mid(str, i, 1) = "A" Or Mid(str, i, 1) = "B" Or Mid(str, i, 1) = "C" Then
        replace_but_ABC = replace_but_ABC & Mid(str, i, 1)
    End If
Next i
msgbox replace_but_ABC
End Sub