My article in the Aug. 2 issue of The News reviewed conventional thermostatic expansion valves (TEVs or TXVs) and covered the basic operation of electronic expansion valves (EEVs). This column will focus on control schemes of EEVs.
EEVs have small stepper motors that open and close their valve port. They do this in response to signals sent to them by an electronic controller. Sensors like thermistors and pressure transducers are wired to an electronic controller and act as feedback devices to the controller telling it what is happening out in the actual refrigeration and air system in a refrigerated case. (See Figure 1.)