Mermaid AC Question

I hope this is the proper spot for an AC question.

If not, someone point me in the right direction,

Here's my issue. The PO has installed, (year unknown) a Mermaid 6500btu AC unit with reverse heat. When I turn it on, the compressor comes on, the fan is blowing. The low side (I think) tubing is getting hot, The compressor is getting hot, no cold tubes anywhere. Eventuallly the comprssor will kick off due to thermal overload.
If I turn it to heat, It hums real loud and pops the main (shore power) ac breaker.

This sounds like a reverse solenoid problem, however, I have read that the solenoid is normally in the cold position not the heat. So it would make sense if the unit was stuck on cool and not Heat.

All the obvious items are working properly. Water, filter, fan, etc.

Re: Mermaid AC Question

You are not getting enough water flow to keep the system cool. Coils should be warm, not hot. Clear the sea strainer and backflush the system.

Re: Mermaid AC Question

Water flow is very good. Like a water hose running outside the boat. The hot copper tube is not the coils, is before that stage. Like from the compressor to the reversing valve. The actual coils are kind of cool, but just barely.

Re: Mermaid AC Question

Sounds like it's out of refrigerant. In heat mode the condenser becomes the evaporator and the evaporator becomes the condenser, the suction line to the compressor will still get cold that is what keeps the compressor cooled. Also the reversing slide valve needs refrigerant differential pressure to assist the spring to change direction.
Look for any oil residue especially around the cap tube, they sometimes will rub thru somewhere.

Re: Mermaid AC Question

You may think the water flow is very good, but it's not cooling. I've been there. Tons of water coming out but the AC keeps kicking off. Mine did this and it was because a film had developed on the interior of the coils and it wasn't transferring heat to the expelled water. This was on a unit that was only a year old. I backflushed the system thru the output portion of the coil and then flushed bleach/soap thru it. You would not believe the amount of crap that came out of the discharge port when I kicked it back on.

This is a free and easy part of trouble shooting that every repair flowchart says to start with. It's up to you.

Re: Mermaid AC Question

Sounds like a good, easy step to try. I've read on some other post that 50/50 mix of phosphoric acid /wter does well too. (and I just so happen to have some)
So I shut off the seacock valve to prevent water from entering the system, disconnect the water out hose from the coils and this is where i pump the cleaning mixture in? or do I simply disconnect the raw water intake, put in a bucket of mixture and let run out the side for a few seconds, let sit and run somemore, then reconnect to raw water?

Re: Mermaid AC Question

First clean the sea strainer thorooughly and reinstall everything. Leave the seacock open like you would normally have it positioned.

Remove the discharge line from the coils and backflush with a garden hose at full strength. You will also be flushing out crap from the raw water pump as well and it will discharge out the raw water intake of the seastrainer.

Reconnect the line, and open the top of the seastrainer again. Pour the seastrainer as full as possible with straight bleach (this does cause someoverflow into the bilge, but only a couple of cups of water). Close it up and run the AC.

Open the seastrainer again and fill with liquid soap (dishsoap). Close it up and run the AC again. This will also clean off the raw water pump impeller.

Repeat until the AC discharge water is clean. You can also pour muriatic acid in there as well, but be careful about the amount you use. If it's too strong, it can have a negative effect with the aluminum components.

As a protective measure, I break apart a 3" chlorine pool tablet and put the pieces inside the seastrainer in a small woven bag. This keeps a constant flow of chlorinated water running thru the system whenever it's on. I haven't had any issues since starting that.

This cleaning may or may not fix the issue, but it's always the first place to start since you'll never have a guaranteed troubleshooting without a clean cooling system.

Best of luck.

Re: Mermaid AC Question

Will have to improvise a little, but I get the jest of it.
Boat is in the water at the slip. No pressureized water there. The system has the cheapy lill plastic strainer.

Re: Mermaid AC Question

No fresh water spigots at the dock? Strange...