Defrost is Default, if you lose vacuum to the system you automatically go to defrost, which means, you constantly have vacuum applied to the actuator for the panel, the actuator is staying actuated after vacuum has been removed or you have a mode door issue.
Unless my info is not correct, the vacuum diagram you showed is for 85-87 Except L-Body.
According to my info this is correct for 85-87 L-Body.
1)Recheck vacuum line routing, there are 3 actuators (see items 14, 20, 24), if vacuum line routing is correct and the problem persists, continue...
![Rectangle Slope Font Parallel Diagram]()
![Font Parallel Pattern]()
2)Disconnect the main vacuum source underhood and see if the air now blows from defrost only.
a)If Yes, you know you have an issue with vacuum constantly being applied to the panel actuator.
b)If No, you have an issue with the actuator binding/not releasing or the mode door is stuck in the "panel" position.
Unless my info is not correct, the vacuum diagram you showed is for 85-87 Except L-Body.
According to my info this is correct for 85-87 L-Body.
1)Recheck vacuum line routing, there are 3 actuators (see items 14, 20, 24), if vacuum line routing is correct and the problem persists, continue...
2)Disconnect the main vacuum source underhood and see if the air now blows from defrost only.
a)If Yes, you know you have an issue with vacuum constantly being applied to the panel actuator.
b)If No, you have an issue with the actuator binding/not releasing or the mode door is stuck in the "panel" position.
