A thermostatic expansion valve (TXV) is designed to maintain a specific amount of superheat at the outlet of the evaporator. If the superheat value is too high or too low, the TXV may be the cause. However, before deciding the TXV is defective, all other system causes must first be investigated and ruled out.
If you believe that the TXV is the cause of a system problem, first try adjusting the valve, following any manufacturer’s instructions. For many valves, you can increase the superheat setting by turning the adjustment stem clockwise, and decrease it by turning the stem counterclockwise. Always check the instructions.