On my 1999 SEL, the front (top) slide switch for the temperature setting for the heat and AC makes a steady clunking sound when I move it off one spot. I am not able to set it for any other position. How may this be repaired? Thank you!!

There is switch on it, maybe in it to move from heat to A/C. then set the arm for the temperature.

Sounds like your thermostat may be stuck open. When the wind moves in front of your car, it chills the Radiator and drops the temperature. All the other settings for Heat, like ductwork and waterflow are in the same positions sitting as moving.

These trucks had a problem with tje ac commpressor clutch breaking i would recomend sliding under truck and looking closely at the ac clutch. also the idler pulleys tensioner and waterpump pulley as these are also problematic

Sounds like a bad relay or blown fusible link.

Air Temperature Control Blend Door Failure No Heat or no AC (dependes on where door sticks)

In all modern cars there is a tiny DC electric motor driven gear drive that moves a plastic door that blends heated and cooled air from the AC and the heater core, this is called (interestedly enough) the air temperature control blend door actuator. The motor that moves this door fails because the door starts sticking from warping, most common complaint is no heat but it can be no AC as well. To replace these parts (blend door and blend door actuator) you must remove the entire dash from the car. Always have this problem confirmed by a dealer or qualified repair shop as it is a very expensive repair.

Other causes of no heat in the cabin are engine thermostats that are stuck open (engine runs cold) or air bubbles in the cooling system.

If the rear is working well and front is not I would suspect a blend door or actuator issue in the front.Double check and see if you can hear anything moving when you are adjusting temperature from hot to cold.Also check and make sure the air flow moves properly from defrost to vents and floor etc.

test the electromagnetic clutch on the compressor pulley for continuity give it 12 volts it should clunk in if not the clutch is either seized or windings gone

what kind of sound? Clunking, squealing?

go here for help

http://groups.yahoo.com/group/villagerquest/

If yours is making the clicking sound then you blend door actuator is bad

Sounds like your temperature actuator is not moving or your temp door is broken. On max a-c ,coolant is shut off to your heater core allowing only cold air in.