Question = The heat in my 95 Lumina works but when I turn the nob to switch from defrost to the vents it doesn't switch it only blows out the defrost and on the floor a little. No matter what I turn the knob to it just comes out them places. Is it some thing to do with a vacuum line. When I turn it to air the compressor kicks but doesent blow cold air.
I don't think its the knob because it makes the compressor kick on so I am confused hope you can help me.
Answer: You have two different problems on your Lumina that may be related to the same thing. The fact that the airflow will not change mode positions means that the control switch in the panel is bad or you have a vacuum problem. The system is vacuum actuated. You should be able to hear a switching sound behind the HVAC control panel when changing the vent positions. If you do, then the problem is either in the line that feeds to mode actuator, the actuator is bad or the door is broken. The mode actuator is the part that actually moves the doors behind the dash to change the positions front vent to floor to defrost. When the system is not working properly, it defaults to defrost as a safety precaution.
The problem with the air not blowing cold could also be because of no vacuum to the HVAC control panel. The temperature door in the dash is also controlled that way with another actuator. But there are other possibilities. Could just be low on Freon, a restricted orifice, temperature door broken etc. With these things all happening at the same time, I would suspect a vacuum problem.
The control head is feed with vacuum from a purple hose that comes from the engine compartment. There is also an HVAC vacuum reservoir ball. The purple hose comes in the dash under the passengers side then goes to the control panel. Check that first. If there is vacuum, then you will need to remove the HVAC panel and see if it is switching hoses as you turn the knobs.
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