I just installed air in my 35 Sonic. I'm having a problem where the aluminum fins on the retun side of the unit are freezing solid with ice after a couple hours of running.

Does anyone know what would cause this? a buddy of mine re-charged the unit to make shure it was good on freon. he also verified i had enough return flow getting to the unit.

any ideas??

could be a number of things....low charge , low airflow(restricted by something or dirty) , low return temp, or a combination of the above....after a few hours what is the temp of the cabin?

why did he check the charge?

Maybe a recycling switch. letting the the compressor not cut off making the condenser freeze up?

last time i checked the digital thermostat before it froze, the temp was 77 (have it set for 73). The reason why we checked the charge was to rule out the low charge theory. And It was a bit low due to a small leak in a schrader valve. (this is a used unit). We put some pipe sealer around the cap and it seemed to hold. he left the gauges on there for 15 minutes and closed the hatch where it is mounted....and the pressure never dropped. So he said my return supply must be good or he would have seen a pressure drop after he closed the hatch.

What kind of refrigerant is this system using and what were the pressures (both high and low side)?

the refrigerant is R22. I forget what the high side was, but the low side was 55 and he charged it up to 68. This is a 7k btu Marine Air unit.

Your talking like this is a split system.....or is it a package unit.
have any pics?

Here is the website for the system.....

http://www.marineair.com/pdfs/vr.pdf

Usually restricted air flow. Either clogged with dust/debris on the intake or kinked hose on the outlet. Also check to see if the fan is running at high speed.
Gary

Sounds kind of odd to have the evaporator freeze up with a suction pressure of 68#. A 68# suction gives you a 40 degree evaporator coil. I can understand the 55# freezing up, that would be a 30 degree coil and moisture in the air would instantly freeze to the coil. Your suction pressure is dropping down below 58# for some reason. Are you sure that you do not have a refrigerant leak and you have lost some refrigerant again. How long does it run before it starts to freeze up. Does the cabin ever start to cool down?