The correct answer is A) "2" should be turned to further compress the spring. To increase the operating head pressure of the refrigeration system, the spring-loaded valve (item "2" in the illustration) must be adjusted to increase the compression of the spring. This will raise the pressure at which the valve opens, resulting in a higher operating head pressure in the system. The other options are incorrect because: B) Relaxing the spring compression would decrease the operating head pressure. C) Compressing the bellows (item "4") would not directly affect the spring-loaded valve that controls the head pressure. D) Relaxing the bellows would also not impact the spring-loaded valve.