Tom, are your units air cooled, water cooled or do they have keel
coolers? If there is a refrigerant problem it will show up by the loss
of frost on a portion of evaporator. Is there at least a thin layer of
frost covering 100% of evaporator? If not describe where frost is not
present. If water cooled do they both use the same water source? Are
these units equipped with Frigoboat’s SSC panel, if so is red LED
flashing? If so what is the flash pattern? If there is a single flash
and four second in between flashes there is a low voltage problem at
units.

Connecting gauges is always a mistake unit it is confirmed the systems
are truly low on refrigerant. The only things common to the two units
would be the boat’s electrical or possibly condenser cooling medium
air or water. If it is true they are both drawing ½ normal power this
would indicate refrigerant problem what happens if one unit is shut
off? Are the compressors hot to the touch.