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Is it your condenser or your evaporator that is freezing up?

Evaporator freeze up may be a symptom of low on refrigerant but not always. When a system is low on refrigerant the evaporator pressure will be lower than normal, and that lower pressure can correspond to a temperature below freezing, but only if there is still enough refrigerant in the system for liquid to be present in the evaporator before boiling off. Often when that is the case the frost will form at the bottom of the coil, or in bands across the coil.

Having said that, most of the time when a system is low on refrigerant it does not freeze up because there is not enough refrigerating effect with the remaining refrigerant to get the coil that cold.

If the coil is freezing evenly over the entire coil face, you may be dealing with a different problem. For example, you say you upsized your raw water pump. On refrigeration systems the head pressure and the suction pressure are related. If the condenser is cooling too much it will cause low head pressure, which in turn causes low suction pressure. Low suction pressure means low evaporator temperature which can result in a frozen coil. When it comes to condensers too much cooling is not a good thing.

Poor air flow will also result in a frozen coil. things like a dirty evaporator, dirty fan wheel, or restricted ducts would be the main culprits.

Then of course there is the #1 cause of air conditioner freeze up: under sizing/setting the thermostat too low. Air conditioners need off cycle time. If they run all day without cycling off because either they cant keep up with the load, or you are setting the temperature lower than it is capable of achieving, they WILL freeze up.

What is the temperature of the supply air before it starts to freeze? What is the ambient air temp? How cold is the suction line going back to the compressor? How cold is the liquid line feeding the evaporator?

I am curious, looking at your pictures it looks like the unit is enclosed in a locker of some kind. How does the unit get return air? In order for any a/c unit to work correctly it needs to recirculate the air in the conditioned space. For every cubic foot of air you blow into the cabin you should be sucking the same amount of air back to the unit. If you are drawing air from another space, cooling it, then dumping it into the cabin the A/C will never keep up.
 
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