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Solved problems · Refrigeration · Crew answer

Why is my boat's 12 V fridge not cooling?

Most 12 V fridge failures on boats are low voltage at the compressor controller or poor condenser airflow. A test LED on the controller shows an error code.

Symptom

The fridge runs warm, the compressor won't start or keeps starting and stopping, and the battery may be draining. You may hear a brief click or hum from the compressor.

Likely cause

Compressor controllers such as the Secop (formerly Danfoss) BD units shut down to protect the battery when voltage at the controller drops below the cut-out setting (10.4 V by default on 12 V) and won't restart until it recovers (about 11.7 V). Long or thin wiring, poor connections or a tired battery cause that drop. Blocked condenser airflow, a failed fan or a thick frost layer reduce cooling; refrigerant leaks are less common.

Stop now if

Wiring or the controller is hot or smells burnt, or the battery voltage is very low. Switch off and charge before running the fridge again. Never open the sealed refrigerant system yourself.

The fix, in short

  1. Read the controller's error code. Many BD controllers report faults by flashing an LED wired to their diagnostic terminals. One flash means battery protection (voltage out of range), two means too many starts or fan overcurrent, three a motor start failure, four minimum speed not held, and five controller overheating.

  2. Measure voltage at the controller during start. Measure at the controller terminals, not the battery, while the compressor tries to start. A big sag means voltage drop: check the wire size against the maker's table, clean and tighten connections, and remove extra junctions or switches.

  3. Restore condenser airflow. Make sure the condenser fan runs, the condenser isn't dusty or blocked, and warm air has somewhere to go.

  4. Defrost and check the seals. Thick ice on the evaporator insulates it. Defrost, then check the lid or door seal by closing it on a strip of paper.

  5. Call a refrigeration technician for gas problems. If voltage, airflow and seals are good and the evaporator never gets cold, suspect a refrigerant leak or a failed compressor. That needs a certified refrigeration technician (EPA Section 608 in the US).

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Refrigeration: 12/24 V variable-speed compressor with electronic controller (for example Secop BD35F/BD50F)
  • Wiring: DC feed sized for low voltage drop

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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