If you had a vacuum problem ,,the only position that the system would work is defrost ,, so i do not think you have a vacuum problem ,,,,
It could be the control head ,,, or one of the vacuum motors is bad ,,, this is what happens when you solect the floor mode
When FLOOR is selected:
- The air inlet door vacuum control motor is at no vacuum, admitting only outside air into the passenger compartment.
- The panel/floor door vacuum control motor is at full vacuum and the panel/defrost door vacuum control motor is at no vacuum, directing airflow to the floor duct. A small amount of airflow from the side window demisters will be present.
- The temperature can be adjusted to heat the air, but air cannot be cooled below the outside air temperature.
- The A/C compressor will not operate.
- The blower motor is on.
based on the above ,,,two doors have to operate to make the floor mode work,,, the floor/panel motor has vacuum ,,,,,,and the panel/ defrost has not vacuum ... so you said that everything else works ok,,,,,,,so this mean we can rule out the panel/ defrost vacuum motor ,,,,, so the only motor we have to check out is the panel/ floor motor ,,,, and see if it has vacuum when in the floor mode ...
so if you pop off the panel on the center lower of the dash ,,, see pic
and from the drivers side , you should be able to access this motor and see if the hoses are conected and if the motor has vacuum , or working ,,
any more info ,,just ask , we can go back and forth on this page