Here is a method to test the function of the servo motor control.
This method will test the servo motor, the motor limit switches and the feedback potentiometer as well as the fan switches ard relay.
This system works by means of a servo motor that operates switches, valves and levers in an attempt to keep the interior of the car comfortable. It is a tinkerers dream and a nightmare to many others. The heart of the system is the "Servo" which consist of gears and cams driven by a small reversible DC motor. There is also an electrical potentiometer, known as the "Feedback Pot", that is attached to the cam shaft and returns a location value to the servo controller, known for some reason as the "Amplifier". In order for our replacement controller to work, the "Servo" and "Feedback Pot" must be in good condition.
This video shows how to test the Servo and Feedback Pot.
You will need an Ohm Meter to test the Feedback Pot