A really good and much under rated feature of the Danfoss BD35 and BD50 compressors are their inbuilt diagnostics function. Before doing anything else with a 12v or 24v fridge that is not working is make sure you test the controller on the Danfoss BD35 or BD50 compressor. The following testing procedure must be carried out.
1. Turn off the breaker (or remove the fuse) supplying DC power to the system.
2. Use a small circuit to link out the thermostat terminals (C & T).
3. Next, connect a small LED to the small + and the D terminals.
4. Turn on the breaker (or install the fuse) to the system watching the LED as you do so.
5. If the compressor fails to start the LED will flash a number of times every four seconds.
Note: The fault code will only be shown when the compressor fails to start or stops.
Interpreting power supply results
Led flashes once LOW VOLTAGE, This means the voltage is falling below the minimum required at start up (10.5v for 12v systems)
Led flashes twice This means there is an error with the fan which is drawing more than 1 Amp and causing too much resistance to the compressor on start. Remove the fan terminals and if the fridge starts replace the fan and problem solved.
Led flashes three times Compressor has a start error, which normally means indicates that the control unit is faulty.
Led flashes four times Compressor overload. System has a blockage, possibly moisture that has entered the refrigeration system or the compressor has siezed
Led flashes five times Electric overload. Again this would suggest that something serious is wrong with the system and you should contact your local refridgeration engineer.
(For more details on the fault reporting see www.FixMyFridge.co.uk manuals section)