So I have a four zone a/c chiller system on my boat. We replaced both chiller units about five years ago and they appear to be working well. I virtually never use my a/c but alas we are having some increased temps up here and I want to use it. The chillers are 2(ea) 5 ton units (10 tons total). The controls are very basic. There is a breaker for each compressor and a toggle switches to put each compressor to cool-off-heat. A toggle switch For the circ pump and then a breaker for each zone. So my stupid question is: when do you use one compressor vs using both? Or are you always supposed to run both? The compressors are plumbed in series and there is one water line loop running through each air handler. There are a total of 6 air handlers. I have the system running currently with just one compressor on and the salon and master Strm zones on. The water in the pipe loop is pretty dang cold and temp is slowly coming down.