The previous owners of my boat all did a great job of keeping manuals for all of the equipment on the boat. The Ocean Marine AC units on my boat, according to the manual, have this three minute delay. The fan does start running when you turn the breaker on, but there will be no water flow until the compressor and the pumps start running after the three minute delay. If your units are Ocean Marine, this might be what is going on. I don't know if other AC manufacturers have this delay. I was worried about damage so had not gotten to three minutes either. Then I finally got around to reading the manual, and found the info about the delay. Had considered the airlock possibility as well.