Air Conditioning Repair Certification (ETI) 2025 – 400 Free Practice Questions to Pass the Exam

The correct answer is that a thermal-electric expansion valve is controlled by a thermostatic bulb. This component senses the temperature of the refrigerant as it exits the evaporator. It contains a liquid that expands and contracts based on temperature changes, allowing the valve to adjust the flow of refrigerant into the evaporator coil. This ensures optimal cooling performance by matching the refrigerant supply to the cooling load, preventing both underfeeding and overfeeding of the evaporator.

While options like pressure sensors and capillary tubes are used in various refrigeration and air conditioning applications, they do not inherently control the thermal-electric expansion valve in the same way that a thermostatic bulb does. NTC thermistors are resistive temperature devices that change resistance based on temperature, but they do not have the same application in controlling expansion valves as a thermostatic bulb. Thus, the correct mechanism of control for a thermal-electric expansion valve is indeed the thermostatic bulb, which plays a critical role in maintaining system efficiency.