The correct answer is B) excessive amount of non-condensable gases trapped in the condenser. When non-condensable gases (such as air) are present in the refrigeration system, they will accumulate in the condenser, reducing the effective surface area for heat transfer. This results in higher condenser pressure, even if the cooling water flow is increased. The other options are incorrect because they would not directly cause a higher condenser pressure if the cooling water flow is increased. A partially blocked thermal expansion valve (A) would affect the evaporator performance, not the condenser. An evaporator coil in need of defrosting (C) would not impact the condenser pressure. A low level of refrigerant (D) could reduce cooling capacity, but would not necessarily increase condenser pressure if the cooling water flow is adequate.