'02 9400i cabin heat

Could be a few things. The cab blend door and actuator are located in the heater box under the passenger seat. You will have to remove the seat and box cover. There will be two actuators in there, one for the bunk, and one for the cab. The cab actuator is most forward one. With the heater box opened up, move your heater control full cold and hot and see if the actuator is moving at all. If it doesn't move at all you could take off the bunk actuator and just plug it in to the cab actuator connector and test again to determine if the cab actuator is bad or not. If it still doesn't move you can try a heater control module. The cab blend door and housing do tend to warp over time since they are just plastic so the door could be just jammed too. All components are easy to change. Just be careful, since most of those parts are plastic they get very brittle over time due to the heat and will break easy.

 

Along with what Heavyd said, you might also make sure that the water valves on the engine heater hoses are all open, sometimes when a person opens them in the cooler weather, they forget that sometimes the cab heater hoses have valves as well as the bunk heater hoses have valves, four valves total should be open if the system is plumbed this way.

 

The control module is just the part with the heater controls in the main dash panel.

 

Yep, I think your right. It should have detentes. If it feels too free it is probably bad.