My 93 300TE climate control functions perfectly with the exception that I cannot get any heat (or any other air for that matter) to come out of the floor vents.

After doing some searching I've decided it's either the vacuum servo behind the radio or a vacuum leak at one or both of the diverter flaps.

Is there a way I can tell which one is the culprit other than replacing the servo?

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1987 300SDL 167k
1992 Volvo 740 140k
1990 Volvo 740 250k
1989 Volvo 240 269k

Anyone want to trade an old Volvo for an '87 300sdl?