I had a keel cooler
Frigoboat system that repeatedly acted up this season until I finally got tired of it and replaced the 15 year old system. Here is what I learned during several repair sessions with marine refrigeration
professionals as they tried to diagnose the problem. You didn't say anything about pressures but I will assume that you are having a similar problem. At random times my high pressure side would go very high while the low pressure side would drop into a vacuum. When the compressor is on the low side should be around 3-5 psi and the high somewhere around 130-150...ish. If the high side goes too high and the low drops into a vacuum you have blockage in the capillary tube. At that point my SSC controller would kick out a 3 blink red light code indicating there was a problem with the compressor, however, it was not a compressor issue. My system was vacuumed out several times, there was no moisture and we had hoped that any foreign matter was also sucked out. After vacuuming the system it would run good for a few days or a few weeks then it would act up again. Here is our theory on what was happening. We believe that the tubing that runs through the condensor (in this case the keel
cooler) had started to deteriorate with age and very, very small scales were flaking off and circulating through the system. The capillary tube is extremely small, the ID being around 4-5 thousandths. Sometimes that scale would flow through the system without a problem but other times it might get caught sideways in the capillary and block the system. At one time it took almost 400psi of nitrogen backflow pressure to clear it. Other times a small squirt of refrigerant did the job. If your problem sounds similar to mine I would be happy to talk to you about it but most likely, if your keel cooler
is older, you will continue to experience problems until it is replaced and unless you are in cold water
cruising grounds I would suggest going to a more reliable air cooled condensor. It was not cheap
but I have been a very happy captain
ever since! Let me know if you want to chat more about it.