Hello, I need some help. I have a 1995 jeep grand Cherokee Laredo 5.2. My Jeep blows heat out of my defroster only when I turn the knob to change to vent. It still blows out defroster I found a vacuum line had came off my vacuum reservoir. I put it back on and still blows out defroster. I also noticed when my knob is on defroster I can turn it clockwise off defroster and it shuts off system instead of turning all way back to off is the switch control system bad.
It is possible that the control head is faulty. I do not think a vacuum leak would cause an issue. The reason would be that Defrost is the default location for the airflow door. There is no vacuum applied when the mode switch is placed in the Defrost position.
How the Defrost, Floor, and Panel airflow operates on a manual system vs. Automatic Climate Control
The mode switch is used to direct output airflow. There are 5 different modes of operation: panel, bi-level, floor, floor/defrost and defrost. Different modes of operation are identified by symbols on the control panel. The switch controls vacuum signals to operate the air outlet doors.