A decrease in superheat causes the TXV to begin to

A decrease in superheat causes the TXV to begin to

• A. open
• B. close
• C. maintain
• D. oscillate

Answer: (A)

The TXV is a flow control that keeps evaporator superheat at a set value by responding to the temperature sensed in the evaporator with its bulb. When superheat drops, the bulb senses cooler vapor leaving the evaporator, reducing the pressure on the diaphragm and, with the spring, causes the valve to open. Opening the valve lets more refrigerant into the evaporator, increasing the rate of vaporization and raising the evaporator outlet temperature relative to the saturation temperature — i.e., increasing superheat back toward the setpoint. So a decrease in superheat triggers the TXV to open.

The TXV is a flow control that keeps evaporator superheat at a set value by responding to the temperature sensed in the evaporator with its bulb. When superheat drops, the bulb senses cooler vapor leaving the evaporator, reducing the pressure on the diaphragm and, with the spring, causes the valve to open. Opening the valve lets more refrigerant into the evaporator, increasing the rate of vaporization and raising the evaporator outlet temperature relative to the saturation temperature — i.e., increasing superheat back toward the setpoint. So a decrease in superheat triggers the TXV to open.