What is this ?
 

Ok so I am redoing my sons 88 pickup and took the dash and ducting apart to clean out the rat colony. Found this on top of the plenum any idea what it does “RPM plus and minus” thought it would be blower motor speed but feel or see no difference any ideas would be great
https://cimg3.ibsrv.net/gimg/www.yot...7963e0ede.jpeg
https://cimg4.ibsrv.net/gimg/www.yot...e53e4ead6.jpeg

AC amplifier.




The knob controls the engine rpm threshold for when the AC compressor clutch energizes