In part 1 of this article, on the fundamentals of head pressure control ("Fundamentals of Head Pressure Control," Nov. 1), we made the case that reducing head pressure lowers the operating expense of the compressor. However, it was also shown that reducing it too much can adversely affect the health and longevity of the system.
We can conclude that the determining factor in deciding what the minimum allowable head pressure should be is the minimum thermostatic expansion valve (TEV) pressure drop (delta-P) required for its capacity to meet the demands of the evaporator load. Once that has been determined, it becomes a simple matter of adjusting the head pressure controls on the system to maintain that minimum.