Testing the sensor of an HVAC actuator

The other sensor is nothing but a potentiometer. One terminal goes to a bias voltage, the other end to ground and the last is the signal wire. However it isn't likely that all 4 actuators all failed at once. More likely is that the jump sent enough of a voltage spike through the system that the HVAC controller failed internally. For testing that you need a scan tool with bi-directional control that can read the systems inputs and then send control signals to the actuators and see what responds. Normally if it's an actuator they will either not respond at all - motor or gearing failure, or they will travel back and forth - loss of the position signal so the system just keeps moving them until it times out and sets a code.

Great info! Follow up question. What commands do I use to test the voltages and then test the actuators?

If you have a scan tool that can control the HVAC module it will have specific tests in it to test the actuators as they are installed. Test wise you pretty much can see all the voltages testing one actuator. The Yellow wire is ground for the position sensor, the Gray wire is the 5 volt reference for it, those are shared by all the actuators up front. The motors themselves use 12 volts and polarity reversal. So if you took the one you took apart and look at the wiring the motor should be a light green and dark blue. If you connect to that and use the hot cold control you should see 12 vols that reverses polarity to drive the motor. If you don't see that then it is likely the controller itself that has went bad. Unless there is no power to the control head itself.