Chevy Lumina Air Blows From Wrong Vents

Question:
1995 Chevy Lumina service engine soon light. The heat in my 95 Lumina works but when I turn the knob to switch from defrost to the vents it doesn't switch it only blows out the defroster and on the floor a little. No matter what I turn the A/C knob to airflow just comes out them places. Is it some thing to do with a vacuum line. When I turn it to air the compressor kicks on but vents 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 with this problem.

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 A/C 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 vacuum mactuator. But there are other possibilities. Your Lumina could just be low on Freon, have a restricted orifice, the temperature door may be broken etc. With these things all happening at the same time, I would suspect a vacuum problem.

The control head in the dash is fed with vacuum from a purple hose that comes from the engine compartment. There is also an HVAC vacuum reservoir ball under the hood that could have a crack in it and is leaking. The purple hose comes into the dash under the passengers side then goes to the control panel. Check that first. If there is vacuum on that hose then you will need to remove the HVAC control panel and see if it is switching from the vent and defrost output hoses as you turn the knobs.

You will hear the air change if it is switching properly. If it is not switching then you will need to replace that vacuum rotary switch on the back of the control panel, or the whole control itself. Not a hard kob, just a few screws to replace it.

Question
2007 Chevrolet Impala. My rear window defogger won't work. I have checked the relay and window grid and both are ok. When I push the on switch the little light comes on. When I had it fixed under warranty they said they replaced a connector somewhere around or under the dash. They said it was a known GM problem something about moisture getting to it. The part they used was #89046970. My problem is where it is located and how to get to it. Thank You.

Answer:
Odds are that the repair under the dash is not the problem again on your Chevy Impala. This connector has a problem with terminals getting hot and sort of burning. It is under the passenger side of the dash. Remove the carpet trim at the passenger side door. As the harnesses go up from the floor to dash, disconnect the large connectors and look for burned terminal / connectors.

Another common cause is that the terminal on the actual grid has come loose. Either on the dr. side or pass. side of the glass. A black connector plugs into a terminal that is soldered to the grid. One one each side of the glass. Look at those. If the connectors on either side of the glass are good, use a test light to check for power at 1 and ground at the other. If power in, ground side OK, then you have some burned grid lines. This grid is also the radio antenna, so 1 side will have 2 terminals.