Dear Boat Doctor,

I installed a Frigoboat keel-cooled system a few years ago. The system worked amazingly well until last summer when I noticed that it would cool down very nicely if the icebox was warm, but wouldn’t maintain the cold. I tried to turn the system off and back on again, but that didn’t help. If I turned the system off and allowed the cool box to warm up, it would refreeze when I started. I worked around the problem by keeping the box warm and just starting it up when I left the dock, but that defeats the purpose of refrigeration. I am not sure if I have a control problem, a refrigeration problem or something else altogether. How do I figure this out?

John Klein

Fort Lauderdale, Florida

Dear John,

I have installed and used a number of Frigoboat system and I think they are close to magic. I especially like keel coolers, which offer great refrigeration with no fans or water pumps to worry about. But every system has its wrinkles.

Most all marine refrigeration systems are based on Danfoss BD-series compressors, the individual manufacturers then integrate a thermostat, some way to dispose of heat (water cool, air cool, etc.), and a plate or evaporator to be placed in the icebox. 

Danfoss compressors are smart devices; they have a built-in diagnostic system to report errors that cause the compressor to stop. The diagnostic status is reported via an LED attached to the system. Many systems include the LED, but you can add one between the “+” and “D” terminal on the compressor.

You didn’t mention if, when the box refuses to cool, the compressor is running or has stopped. If the compressor has stopped, you may have a compressor or thermostat problem.  I’d start by jumpering out the thermostat: just place a wire between C and T, this will force the compressor to run continually. If this fixes the problem, you have a thermostat problem. If the compressor still stops, you will need to look at the error code on the LED. The codes are listed below. If your compressor is flashing a code, I’d expect a 1 or 3, and these typically both mean an issue with the voltage supply to the compressor.

1 – Low-voltage error

2 – High fan current error

3 – Compressor start error

4 – Low speed error

5 – High compressor temp

You could also be experiencing a refrigeration problem. The Frigoboat system uses a capillary tube system to meter the refrigerant. This is a tiny copper tube that the refrigerant flows through. If your system gets a tiny bit of moisture or debris in it, that tube can become clogged or intermittently clogged. I suspect you may have a little moisture in the system, and when the system gets cold the moisture freezes in the cap tube and blocks it. When the system warms, the ice melts, and the system works again.  I would suggest you contact Frigoboat and add a filter/drier.  This is a device that will remove the moisture and/or debris.