Question 134Refrigeration & AC - 1st Asst/Chief

The correct answer is A) an increase in sensing bulb temperature. The thermostatic expansion valve in a refrigeration system is designed to maintain a constant superheat at the evaporator outlet. When the sensing bulb temperature increases, the pressure inside the sensing bulb also increases, causing the diaphragm to flex downward and further open the thermostatic expansion valve. This allows more refrigerant to flow into the evaporator, increasing the cooling capacity and maintaining the desired superheat. The other options are incorrect because: B) an increase in evaporator pressure would cause the diaphragm to flex upward and close the valve, C) a decrease in sensing bulb temperature would cause the diaphragm to flex upward and close the valve, and D) increasing the superheat setting would cause the diaphragm to flex upward and close the valve.