92 heater problem

is there a usual sight of failure in the vacuum system that controls heater/defrost etc? my 92 only has defrsot and nothinh else do I need to tear the dash apart or what? anyone have a diagram of this?? Thanks, John

John, the heater defaults to defrost. You need to check under the hood for any vacuum hoses off or cracked. Listen to the heater control when you slide the mode switch, you should not hear any vacuum , if you do you may have a bad switch but usually it is a hose cracked by the vacuum resevour under the hood.