problem winterizing a/c system

JamesG161 · Nov 12, 2019

Since both lines discharge above the water...
Drain the lines at the Tee

Empty lines don't freeze.

Jim...

Rich Stidger · Nov 12, 2019

That is a puzzlement for sure. But I've learned that many boat issues don't make sense.

I also have two A/C units, a 16 and a 5 like you. It sounds like we both have the same setup. I assume that the A/C systems are operating properly and that the main 16K unit shows a discharge and is not blocked. Given that is true, I can't think of any reason why you can't get AF to run through it. I suspect that the AF will flow from the 16K unit, but due to more flow resistance (for unknown reasons) it takes much longer than you expect.

The first year I winterized my systems, I found that a huge amount of AF was wasted out of one discharge while waiting for the other one to show AF. I solved this problem by adding two shutoff valves so that I could force the AF through one A/C unit at a time. This cut my AF usage by probably half. In your case it would also force the AF through each unit independent of the other. That should solve your issue.

For this year, you could simply disconnect the lines from the pump tee and drain as Jim has suggested above. To insure that you got all the water out from any unseen low spots, you could pressurize the lines with a compressor or a dinghy air pump, or you could attach the lines to a wet shop vac and suck out the water. Your choice, whichever is easier for you. For an easier time next year, read on....

In this picture below you can see the two 1/4 turn valves I added. The tee and check valve noted at the bottom are for a take-off to the anchor washdown pump and to the galley seawater faucet, and have nothing to do with the A/C valve arrangement.

Rick486 · Nov 12, 2019

richk said:
I have a boat with two of a/c units, a 16 and a 5. While winterizing I can get the antifreeze to flow through the smaller unit but not the larger. They both have the same feed which splits after the pump.
Any help is appreciated.

I have seen this on my boat in winterization. When I broke the hose connection at the raw water strainer to attach my antifreeze bucket, air was allowed to enter the line upstream of the A/C circulation pump which feeds both units. The aft unit is much closer to the pump and the discharge is lower in elevation. So I worked around this by closing the aft outlet, disconnecting the forward discharge hose from the discharge fitting in the hull, and applied suction to remove the air. Works fine.

Parsons · Nov 12, 2019

Since the flow problem seems to be after the pump and there is freedom to equalize pressure at the T-joint, can't you just force the anti-freeze to go to the other AC cooling unit by back-pressuring the flow from the smaller AC unit? By back-pressuring, I mean shove a stopper in the outlet that is draining to force the pressure into the larger AC unit. There is nothing other than piping between the pump and the outlet for an AC, so you cannot damage anything if using the normal pump. This would solve the problem for this year's winterizing without cutting piping and installing valves.

For next year, I'm all for @Rich Stidger 's more elegant valves. That would mean you could winterize without leaning over the rail.

Rich Stidger · Nov 12, 2019

richk said:
Report
<snip> The system worked in late September...maybe algae buildup on the 16K side?

I agree that it is most likely a partial or total air lock. I too have seen that happen, but in my instance the entire system was air-locked at the pump.

JamesG161 · Nov 12, 2019

richk said:
maybe algae buildup on the 16K side?

I put two 1" Chlorine pool tablets in my strainer to kill the algae/slime layer and prevents other stuff like barnacles build up on the water side of the heat exchangers.

But...

If it was crap on the 16k unit side, it would have had trouble keeping the boat cooled/heated.
Jim...

PS: The Dometic/Marineair exchangers use the same copper/nickel material that is used in spa/pool applications.

NYSail · Nov 12, 2019

or you can just pump the antifreeze in through each discharge hose......

First year winterizing I had a problem with my larger unit.... would not let anything through hose even though flow worked perfectly when unit was turned on.... And I tried pumping through both ways to make sure there was no check valve shutting.

Good luck.

Bob R. · Nov 12, 2019

Rich, you should have separate sea water discharge shutoff valves at the discharge through hulls for each AC unit. I shut each discharge valve separately and flushed antifreeze through each unit separately.

Rich Stidger · Nov 12, 2019

Bob R. said:
Rich, you should have separate sea water discharge shutoff valves at the discharge through hulls for each AC unit. I shut each discharge valve separately and flushed antifreeze through each unit separately.

Both discharge thru hulls are well above the water line. I may be wrong but I don't think it is standard practice or normal building code to require seacocks at those type of discharges. Even if the boat were heeled to put those discharges under water, the other end of the A/C cooling loop is underwater as well for water pickup. There would be no risk except if a hose came off the thru-hull, and that would be a short-lived event. So I don't see the risk. But if you have them and feel good about closing them, then continue your practice.

Rich Stidger · Nov 14, 2019