The electronic expansion valve (EEV) operates with a much more sophisticated design. EEVs control the flow of refrigerant entering a direct expansion evaporator. They do this in response to signals sent to them by an electronic controller. A small motor is used to open and close the valve port. The motor is called a step or stepper motor. Step motors do not rotate continuously. They are controlled by an electronic controller and rotate a fraction of a revolution for each signal sent to them by the electronic controller. The step motor is driven by a gear train, which positions a pin in a port in which refrigerant flows.

Step motors can run at 200 steps per second and can return to their exact position very quickly. The controller remembers the number of step signals sent by the controller. This makes it possible for the controller to return the valve to any previous position at any time. This gives the valve very accurate control of refrigerant that flows through it. Most of these EEVs have 1,596 steps of control and each step is 0.0000783 inches.

The electronic signals sent by the controller to the EEV are usually done by a thermistor connected to discharge airflow in the refrigerated case. A thermistor is nothing but a resistor that changes its resistance as its temperature changes. Other sensors are often located at the evaporator inlet and outlet to sense evaporator superheat. This protects the compressor from any liquid floodback under low superheat conditions.

Pressure transducers can also be wired to the controller for pressure/temperature and superheat control. Pressure transducers generally have three wires. Two wires supply power and the third is an output signal. Generally, as system pressure increases, the voltage sent out by the signal wire will increase. The controller uses this voltage to calculate the temperature of the refrigerant with the use of a pressure/temperature table programmed into the controller.