Slipping fan clutch.
A slipping fan clutch would not affect ram airflow. This problem will reduce airflow at low speeds causing reduced air conditioning performance at low speeds.
Proper condenser airflow.
Reduced airflow across the condenser would elevate both the high and low side pressures. Airflow across the condenser is created by vehicle movement. A fan clutch allows the fan to freewheel when ram airflow is greater than the fan induced airflow. A slipping clutch would not change ram airflow.
A locked up fan clutch.
It is also common for a fan clutch to lock-up which will cause problems for the water pump, the belt drive, and the engine’s horsepower output. A locked up fan clutch will not reduce A/C cooling efficiency. Reduced airflow across the condenser generally affects the ability of the condenser to cool the refrigerant, resulting in higher temperatures and pressures in both sides of the A/C system.