A/C Raw water intake

[Boots]

I am looking at fitting a Webasto A/C units, and wonder if I could double up on one of the other through-hulls, rather than poking another hole in the bottom. The toilet flush is seldom used, and the valves in the head should stop air from being pulled in, in the case of an external blockage. Any thoughts on this?

[a64pilot]

I just installed a second AC a week or so ago, I tied into an existing seacock that currently supplies both heads and the engine, actually I tied into the line going to the fwd head as it goes right by the AC.
When the engine is running, it pulls enough vacuum to pull air back through the AC line and the pump will lose prime. It's not nearly enough to cause engine cooling problems.
To combat this I installed a ball valve in the discharge line where I could easily access it

[gonesail]

the valves will prevent the AC from sucking any air thru the head pump. i did it (spliced into the head intake) on my boat and never had an issue. be sure to use bronze fittings at the seacock.