Frigoboat units are generally excellent and reliable, but they are prone to an occasional buildup of moisture and compressor oil
that can bung up the capillary tube coils, particularly in the vicinity of the evaporator.
This will cause an intermittend fault which will be easily masked by any tampering with the pressures of the gases, as offgassing and refilling will tend to force the oil/moisture into a different location or diffuse it temporarily. What tends to happen is:
1. Unit "runs" but only cool to touch, no frost on plate and no joy to owner.
2. Owner frets that it is the compressor, or the keel cooler, or the gas pressure.
3. Owner gets "refrigeration engineer" onboard, who spends a lot of time and a fair amount of the owners money.
4. The system cools down! Owner is pleased. Beers are had cold. All is well with the world…
5. Problem returns… go to step 1.
This is because the problem of moisture/oil in the system is finicky, can come and go, often masquerades as some other issue, and is hard to resolve satisfactorily. Many actions of rectifying or tinkering with other aspects of the system may well relieve the problem… temporarily.
I am not saying this is definitely the case in your case, but I have had a lot of adventures and miseries with these systems, which as I said are wonderful when working. It may be something else. But in the cases I have experienced (a good number), ultimately the problem is an inadequately sized or disfunctional inline drier.
These components are not necessarily cheap
, but are easy to replace and should be larger than may appear necessary for a system which is operating of has operated long term in the tropics.
You may have joy with a high pressure pump aspiration of the system. But IMHO this will never be fully effective until and unless you replace the inline driers. If you are trying the aspiration option, running a hairdrier over the capillary tubes while the suction is ongoing is a good way of encouraging escaped compressor oil
or recalcitrant moisture in the system to flow more freely or evaporate.
Hope this helps.