The slide pot. is located on the end of the temp. control lever. You can get to it by removing the knobs and the plastic faceplate on the Auto A/C dash control. A flashlight will help you see the pot.. Attach one end of the plastic tube that comes with the can of contact cleaner to the nozzle on the can and insert the other end into the pot. on the temp. lever. Give the pot. one or two small shots of cleaner and then move the temp. lever side to side to clean the internal contacts. You don't want to spray the outside of the pot., just the inside.
A slide potentiometer, or slider as some techs. refer to them, is a variable resistor that functions by moving a sliding stem. A good example of such is the "sliders" on a mixing board used by recording studios, etc..
A rotary potentiometer is round shaped and varies resistance by turning a shaft that generally has some type of round knob. In the case of the MKII Auto A/C system, the temp. control pot. sends a signal to the input stage of the A/C amplifier, which in turn controls the two tiny solenoids inside the DVV. The rotary pot. is connected to the stem on the power servo and provides a feedback signal to the A/C amp. which lets the A/C amp. know the position of the power servo stem. The whole system works in a closed loop fashion so any poor contact in either of the two pots. will cause the input/output signal voltages of the A/C amp. to become erratic and cause the A/C amp. to switch the DVV On and Off in a less than desirable fashion, thus the very annoying clicking that you hear from the DVV.