Turning the thermostatic expansion valve adjusting stem clockwise would have which effect on operating superheat?

• A. Increase superheat.
• B. Decrease superheat.
• C. No change.
• D. Open the valve fully.

Answer: (A)

Clockwise turning of the thermostatic expansion valve adjusting stem increases the spring pressure on the valve mechanism. That higher spring force makes the valve require more evaporator bulb pressure to begin opening, so the valve opens less for a given condition. With less refrigerant reaching the evaporator, the liquid that does enter is used up more, and the vapor leaving the evaporator is hotter relative to its saturation temperature, which means the operating superheat increases. So the adjustment clockwise raises superheat. If you turned it the other way, the valve would open more, increasing flow and reducing superheat.