Hi, I have a 1992 SeaRay with two heat pumps for AC and heat. Can some one tell me what the plumbing is like? I assume the water is pumped to both units in tandem regardless of which one is turned on. When I turn on the forward unit it pumps water heats and cools. When I turn on the aft unit no water is pumped, the blower turns on but it doesn’t heat or cool. When I turn on both, the forward unit operates fine, but the aft unit just blows room temp air. Thoughts?