1975 450 SLC. When AC turned on, cool air comes out off center vents but heat comes out off both the right and left vent. Help please, Harold

There are 2possibles ,1. The heat / cool slide control is defective, it is not possible to repair. Most likely the servo motor that opens and closes the air vent that gives you heat or cool is stuck. Open your glove box and you will see 2 rubber tabs that hold the door at the open and down position. Push down on your glove box door until it swings all the way down (this wil be past normal open) up inside you will see a metal rod affixed to a arm that pivots via the servo left is full vent(cool) right is full heat. Push your hot/cold heat selector and see if it moves. It may not be moving its full extension. If your not sure push it right and you should get heat push it left and you should get cool check YouTube this is a common problem for this era of Buicks, good luck Bret

The flap that directs the airflow between your front defrost and those Center vents sounds like it is become disconnected from your control

look under dash to make sure vent door is working proper

Take to Midas,they also do a.c. work,they do mine and give a warranty and good price.

This model has a rear heat/cold blend door actuator. Its an electric motor that moves the duct door from hot to cold. When they wear out, they're usually stuck on the last setting

add freon and test

you need to check under dash to make sure plastic heat pipe is in place to that vent

Hi there, Sounds like a vent door switch. It's in your dash and it controls the vent door opening and closing and to which duct the air goes to, defrost, face vents, floor. Best thing to do is buy a Haynes or Clinton's repair shop manual at your local AP store for your particular vehicle. Then read up on it in the trouble shooting section or the step by step RR section. You can purchase these at your local Auto Parts store or buy them on line at ebay burdfrenzy

Hey, what setting is your A/C on Max AC? AC? Cycling air in vehicle or taking it from outside

The car icon on the right in this image is what I'm referring to when I say cycling air in vehicle.


Also, do you ever have cold air blowing? on any setting or any speed? if not, find your A/C fan, it is smaller the the engine cooling fan, sometimes there are 2 fans together. The AC fan should be located at the front of the vehicle and is usually electrically powered.

Also try to find your compressor, looks something like this:


is it running? is one pipe hot and one cold? (the pipes I am referring to are inlet and outlet pipes of the A/C compressor unit.)

Hope this helps, keep me posted

make sure the control knob on the dash is on "RR". This lets the driver control all the vents in the back. The heat only comes out of the floor vents, if you have the knob on the blue dots that represents the air conditioning in which the cool air will come out of the vents up above in the back. There is also an area on the control knob on the dash where you can turn the knob to shut the heat and air conditioning off. If the knob is in this position then you can control everything with the knob up above the seat right behind the driver's seat.