Over the weekend my AC (Mermaid) stopped cooling. It worked fine all weekend. I turned it on late Saturday afternoon and the compressor comes on and no cool air comes out. I check coils they are not iced up. They are not even cool. Compressor runs. What's going on here?

Water running through the unit?

A common occurrence in boat air conditioning is the water pump can easily lose its prime. Some boats, after running can lose pump prime.

Or it might be time to clean the strainer.

Any time the air conditioner is running, check and make sure you have water running out of the discharge thru-hull, which should be above the waterline.

If you find that the water is not running, you have to re-prime the pump which is fairly easy. The pump is a centrifugal type, so it cannot prime itself. The pump should also be located below the waterline.

But since Mermaid are generally aftermarket installs (I suppose some are OEM), the pump may not be located in the best location.

The easiest way to prime the pump is to remove the fitting on the top of the pump, pour water into it, and run it until water comes out. Then simply re-attach the fitting.

If the pump is low enough, simply removing the fitting will cause water to flow through the pump.

If you find you have this problem often, you might want to investigate adding a valve or tee fitting to make it easier to prime.

Then if the pump won't run water, you either have a clogged screen or a bad pump. But also make sure the pump is receiving power. Its AC powered off the Air Conditioner, so a relay could be bad as well in the AC unit.

Mermaid has excellent customer service and a tech support desk to help diagnose the problem, so you can give them a call if needed.

Also, even if you get the pump running, you may have overheated the compressor. In that case, there is a thermal overload breaker located near the compressor. It is a red booted push button switch, and you may need to reset it to get the compressor running again.

My air conditioner in the old boat was a Mermaid, and this is what I recall.

Are you sure the compressor is running, and not just the fan?

Pumping water, compressor coming on, not freezing up, coils not getting cool, has electric heat, and was working fine 6 hours before.

I am sure you are meaning when the compressor is coming on, you are hearing that distinctive sound.

On our old boat, I know that we could adjust the delay time from when the air conditioner started to when the compressor started.

But you said it was recently working, so I am going to rule out that kind of setting.

I guess the only thing I could suggest is to make sure the thermal switch is pushed in (should be a red covered switch on the compressor coil). Otherwise, it might be time to call Mermaid. As I said, they have a nice tech support staff, and are geared to the individual boatowner.

http://www.mmair.com/support/troubleshooting

If you compressor is running, the pressure switch isn't the problem.

Is it a heat pump? Reversing valve could be stuck or the check ball (if so equipped) could be leaking by. Got gauges?

I think I read electric heat. On my Mermaid unit, I also had electric heat, which was accomplished by a separate heater coil behind the evaporator. There was no heat-pump capability.

Yes, I was referring to the high pressure switch; and there is only one that I am aware of, and it has a red boot over it. For sure, if it was tripped, the compressor should not start.

If the compressor runs, then I am assuming all of the relays and compressor-starting circuits are OK.

I am no AC expert, but I think its quickly narrowing down to something like loss of refrigerant.

It was a coolant leak. Hole in coil caused buy coil rubbing, caffing or vibration in an internal part.

Glad you tracked it down.

I believe Mermaid has a 5 yr warranty.

Out of warranty one year. Mermaid said they would put a new coil in it, clean cooling system and recharge for about the same cost as two estimated I got to weld hole. That includes shipping both ways. Of course I have to remove it. Before I ship to Mermaid I will bring unit to the local Mermaid dealer to take closer look at the job and make my decision then.

When I bought my unit a few years ago(6,500BTU) it cost $85 to ship one-way via UPS. Assuming the cost has not gone down, you might find that a local repair might be the least costly.

Like I said two guys quoted me $300-$400 to weld it. The one repair shop is authorized Mermaid dealer in Balt but did not give the same offer as the Mermaid headquaters in Fla. Both said said they would just weld it. But Mermaid said $345.00 for new coil. $60 shipping each way UPS ground included.

Personally, i would get the new coil. If it has rubbed through here, hard to tell the condition of the remainder of the coil.
Also, having refrigeration repairs done by the factory under controlled and proper conditions is a plus.
Those little tubes that make the coil right there under your arrow are very thin. You can weaken that copper easily by welding/brazing near them. I've never been a fan of patching a coil unless necessary.
My opinion only, take it for what it is worth.