Marine A/C

Is the water pan draining, if not water can splash on the lower part of the fins and cause them to ice up? The best way to thaw them is to leave the fan on high (a/c off). If the water pan is draining only about 3 things can cause the unit to ice up. Low on freon, dirty coils, and poor airflow (dirty filter, vents mostly closed).

In the meantime after they thaw, leave the fan on high when using the a/c until a tech can get out.

I've seen coils so clogged with cat hair that virtually the entire thing was a block of ice. Check the drain, let it thaw, clean the coils with a spray designed for that, and back to normal. I have used coil cleaner spray from Home Depot at home, but not on a boat. I don't see why that would be a problem unless the runoff is an issue.

Go ahead and start it after making sure it's clean. There should be a screen across the evap.

If it's been a long time since it's been looked at by a real A/C tech, then consider calling one in. Evap stations can also freeze up on low freon levels.

Thermostat set WAY low where the compressor continuously runs with no chance of cycling?

One last thing I remembered; A ways back a customer complained about their system freezing in the late afternoon / earl evenings. The heat of the day was already dropping. All was clean and all checked out very well.
BUT; she would open the saloon door while she was cooking. Super humid air would go thru the evap and freeze it up in about 45 minutes. Steam from her cooking did the same. The PassPort display was mounted near the kitchen. Heat from the open door and the cooking would keep the compressor running,
I installed a remote temp sensor and a galley exhaust fan. Years later, no more freeze ups.

You have a window open last night?

You have a gas leak and therefor low pressure. It's the main cause of ice.

Icing up is usually a sign of low gas pressure or restricted air flow due to dirty air screen or coil.

If the filter was filthy, Clean it and try again.

+1 AND I had success just by moving the sensor (looks like about the size of a AAA battery on the end of a 6 ft tape). But mine was a 1996 MarineAir unit. Good Luck!

Seconding rcrapps on clean and try again. If the coil is dirty too, clean that as well.

May also help to set the fan to run continuously, rather than cycle on and off with the compressor--especially on hot/humid days