How does a TXV respond to cooling demand?

• A. It changes compressor speed to meet demand.
• B. It alters condenser pressure.
• C. It changes refrigerant density in the evaporator.
• D. It adjusts refrigerant flow into the evaporator by sensing evaporator superheat.

Answer: (D)

A thermostatic expansion valve meters liquid refrigerant into the evaporator based on evaporator superheat. The sensing bulb at the evaporator outlet monitors how hot the refrigerant becomes after absorbing heat. This temperature (superheat) affects the valve through a diaphragm and spring mechanism: if the superheat is too high, the valve tends to close a bit to reduce flow; if the superheat is too low, the valve opens more to allow more refrigerant in. By continually adjusting the flow to keep the evaporator at the desired superheat, the TXV meet the cooling demand efficiently and protect the compressor from liquid slugging. The other options don’t describe how a TXV regulates flow—it doesn’t change compressor speed or condenser pressure, and it doesn’t directly alter refrigerant density in the evaporator.