Another email question on Frigoboat’s keel cooler refrigeration condenser problems

[Richard Kollmann]

My boat was on the hard for 2 days and Frigoboat keel cooler system ran fine for about one week. However, yesterday it suddenly stopped cooling almost completely although the compressor was running constantly. The cap tube line was also noisily vibrating. After turning the fridge on and off a few times it has started working again and the cap tube line is no longer vibrating.

First this Danfoss compressor was not designed to operate at high temperatures that can cause oil and internal electrical insulation deteration. Seawater cooling by keel cooler condensers is only efficient when seawater temperature is no warmer than 75 degrees F (24C) and compressor temperature remains expectable below 130 degrees F (54C).

Water cooled and air cooled hermetically sealed electrical compressors depend primarily on heat removal to be absorbed by much cooler refrigerant returning from cold evaporators. Danfoss designed these compressors to be installed on fan cooled condensing units so that fan air would supplement refrigerant cooling of compressors. Fifteen years ago when water cooled keel cooler BD compressor system started failing I recommended adding another fan just to cool compressor when in tropical weather. Later Frigoboat added a second optional air-cooled condenser to installed in series with the keel cooler.

ANSWER
To explain and answer your confusing experience of lack of cooling and vibrating cap tube line for some unknown reason there was either a refrigerant flow problem of temporary blockage and that blockage helpfully is now captured in filter attached to compressor return line.
If the vibration was continuous for a while all refrigerant in system may have been reduced to vapor gas mixed with drops of liquid. The condenser type air or water is designed to see that mostly condensed liquid reaches orifice of cap tube. Because Frigoboat’s normal keel cooler condenser contains such a small amount of refrigerant and compressor may be very hot this could also explain your temporary problem.

I would not worry about your past two days experience on the hard if amperage draw is now normal and evaporator frost cover is 100%. I would also not run refrigeration without adequate compressor condenser cooling.