Hi everyone,
I work on a ship in australia with a 3 cabinet system (freezer, fridge, fridge) with a redundancy compressor setup(only run one at a time) and seawater cooled condensors
I'm by no means a refrigeration tech, only fairly basic understanding of the systems.

Problem #1(may explain question two)
In the past the system was set up in a way that we could;
isolate power to the compressor in use;
Close HP and LP valves on that compressor;
open the HP and LP valves on other compressor;
run system as normal
since some work has been done weve been told we need to suck down the gas from the compressor in use before we can change over, I dont 100% understand how to do this properly and the fundamental reasons why.

Problem #2 The Freezer and Main fridge "seem" to be operating correctly but the secondary fridge is icing up at the TX valve(if i touch it with moisture on my finger it will stick me to it) and the air from the evaporator fan is no where near cold enough. We have a HP gauge and LP gauge at the compressor units but i dont have one handy to connect to the Schroeder near the TX valve, however i do have an infrared thermometer.

After a bit of reading on here im thinking if there was in issue with refrigerant levels then there would be an issue across the whole system and the pressure levels(at gauges) are consistent with past records. This leads me to think i have to adjust the TX valve in the secondary fridge..
Am I on the right track here or am I out of my depth?
Were at sea at the moment with reception, a possibility of calling a technician out but would prefer to resolve the issue myself.

Cheers in advance,
Mark