Front heat does not heat..but the back heat does..

The most common problem is a stuck or faulty blend door under the dash.

Sounds like your heater coolant hose door flap is broken or loose. May want to check behind the heater controls, if your components are mechanically operated. If electronically, may need to perform more troubleshooting before replacing this component.

how to do fix or change the switch on the dash for ac/heater in a 1989 buick lasbre

There are a number of things that cause this lack of hot air problem. Let me ask some diagnostic questions. Is the engine reaching normal operating temperature? If not replace the engine thermostat. Are the two hoses going to the heater core under the hood at the firewall hot after driving for a few miles? if not the heater core is plugged, remove the hoses carefully and flush it with a garden hose in both directions. Does the AC blow cold but there seems to be no change in the air temperature when you set it to hot air at the dash register vents? If the thermostat is ok, the heater core is not plugged then you likely have a defective air temperature control "blend" door problem, this door moves back and forth between the heater core for hot air and the AC evaporator core for cold air or blends the two airstreams for the desireed air temperature, it is operated by a small electric motor called a stepper motor (stepper refers to a motor that can maintain a constant position) or the blend door is stuck or hard for the stepper motor to move, both problems are common and both parts must be replaced. To replace the blend door and blend door actuator motor requires that the dash be removed from the car and the heater.AC duct work be opened up. On a scale of 1-10 for 10 being the most difficult this is likely a 8 or 9. The job takes about 10 hours in a shop and about 14 at home.

Please rate my help for Fixya, it improves my status and it is all I ask for my time helping you with your problem. Thanks

You seem to be on the right track. You can manually jump the compressor clutch, to come on and see if she blows cold air. Follow
the compressor clutch wiring back to the evaporator. There should be
a 2 wire harness there with a connector. Take the wiring connector off
and install a small jumper wire between the 2 terminals. this should
automatically make your compressor clutch engage , regardless of
freon level or head pressure switch condition. You may also have a
vacumm leak, which controls your heater damper actuator. Check all
the vacumm hose in the engine bay and try to locate the damper in
the dash, so you can manually pull the damper open, to see how it
helps your situation.Good luck.

Sounds like there is a foreign object in the heater case. The only way to reapair it is to remove the object by possibly removing the heater case.

Your Blend / mode door inside the heater ac blower box. is stuck or not moving completly into place.

If this noise is a clicking sound and is coming from the front center of the dash, then it may be the blender door motor which will require removal of the dash to replace it. It will keep the door from switching from heat to a/c. Does the odor smell like you have a freon leak in your a/c evaporator core or does it smell like a rat stuck in your heater and a/c ducts?

Sounds like a stuck heater core valve. Find heater core valve. Under hood, find the two heater core hoses going into firewall. One of the hoses has a valve. Operate temperature control (full heat, then full cold) check that valve changes position. If not either replace valve or control system failure. Also, when temperature control in cold position, one hose should feel hot and the other cold. Temp fix: disable valve to close no heat or on heat.

replace the temp door actuator motor,it is up under the dash ,a flat square block looking thing with 3 screws holding it on u will see two the one u need to change is usally on the bottom