Air Conditioning Repair Certification (ETI) Practice Exam 2025 - Free Air Conditioning Repair Practice Questions and Study Guide

A thermostatic expansion valve (TXV) plays a crucial role in regulating the flow of refrigerant into the evaporator of an air conditioning system. Its primary function is to maintain a constant evaporator pressure by adjusting the flow of refrigerant based on the cooling requirements and the temperature of the incoming refrigerant vapor.

When the load on the evaporator changes—due to varying indoor temperatures or other factors—the TXV responds by modulating the amount of refrigerant allowed to enter the evaporator. If the evaporator temperature decreases (indicating that more refrigerant is needed to maintain cooling), the valve opens wider. Conversely, if the temperature increases, the valve closes slightly to restrict flow. This ability to adjust based on the evaporator conditions ensures optimal performance and efficiency of the air conditioning system.

This function is essential for proper system operation, as it helps avoid issues like refrigerant starvation (too little refrigerant causing inefficiency and potential damage) or flooding (too much refrigerant reducing system efficiency). Thus, maintaining a constant evaporator pressure ensures that the air conditioning system can effectively absorb heat from the indoor environment and deliver cooled air efficiently.