ESCO Refrigeration Practice Test

When evaporator pressure rises, the sensing bulb’s pressure increases and pushes on the AXV diaphragm in a way that reduces the valve opening. The thermostatic expansion valve is designed to meter refrigerant so the evaporator operates at the desired pressure and superheat. By closing a bit, it decreases refrigerant flow into the evaporator, helping bring the pressure back down to the setpoint. Opening would allow more refrigerant in and push the pressure higher, and simply maintaining the current position or causing oscillation isn’t the normal corrective action for a straightforward rise in evaporator pressure.