First, the reason we control head pressure (or more correctly, condenser capacity) is the need to maintain a minimum pressure differential across the orifice of the thermostatic expansion valve (TEV) so that the TEV's capacity can match the load.
In regions where ambient conditions vary widely, or where there are large load variations, head pressure control is an important issue with air-cooled condensers. Because of the importance of the issue, this article will examine some of its implications for the design and commissioning of systems.