Question: This past year I added an air-conditioning system to my boat. Now that the cold weather is here I’m in the process of winterizing things and need your advice. My boat yard says the best way to winterize the sea water system on my AC unit is to force compressed air through the system to push any water out, thereby eliminating any freeze-up risk. A friend of mine who works in the AC and refrigeration business says the best way to be sure all is well is to pump environmentally safe anti-freeze through the system. What’s your advice on this? I don’t want to risk damaging my new system.

It's important to prevent the cooling water between your through-hull and your marine air-conditioning unit from freezing in winter.

Answer: This is a question that comes up fairly often. Dometic Corp., perhaps the largest distributor of marine and RV air-conditioning units in the world, allows for several methods to be used with its units, among them using pressurized air to force water out of the system through the overboard through-hull fitting for the system.

Personally, I prefer to see potable antifreeze pumped through the system. This method will ensure that any water trapped in low points within the system gets displaced by antifreeze solution. Dometic allows for either method in its instruction manuals, but does seem to favor the anti-freeze method over the pressurized air approach in its recommendations.

- Ed Sherman