RE: Danfoss no start-up
Failure to complete a start up cycle is a common report on the Danfoss BD compressors. These 12/24 volt compressors have a brushless motor inside that is controlled by an external electronic module. There have been many different upgrades to these modules through the years so the control functions do vary from one series to another. The job of the module is to cause the motor armature to rotate at a given speed and stop the compressor if one of these operating conditions exists: • Low voltage • Fan circuit overload • High amperage overload • Compressor temperature below freezing Some modules may have other functions, I believe the first three are common to all Danfoss manufactured modules used on BD compressors. The report is that the compressor fails to start. As in all troubleshooting, you start with the simplest nondestructive testing first. If the system operates normally at times, this will rule out a refrigerant flow problem and therefore not require a refrigeration repairman. Low voltage is the most common cause of start up problems. Low voltage can be traced to low battery voltage or the boat’s electrical circuit. The only way to insure that it is not a voltage problem is to connect a full charged battery directly to the electrical module with proper sized correct polarity jumper cables. The older model BD2.5 and BD3 compressors can indicate a low voltage fault with a LED if one is installed between module terminals C and D. Newer compressors BD35 and BD50 have a full function computer chip like your automobile. You can learn more about LED trouble shooting by viewing the slide show on my web site. There are several sections on all these compressors in my 12/24 Volt Refrigeration Manual. The fan circuit overload will stop the compressor if the fan is faulty. There is a separate set of 12 volt + and - terminals on the module that powers the fan for cooling when the thermostat closes. This fan circuit on older units is limited to a maximum of one amp and ½ amp on BD35 and BD50 compressor modules. To eliminate this circuit as a cause for a false compressor start, disconnect the fan wires and any other units connected to these terminals. When eliminating the fan make sure that the thermostat wire is not removed from C terminal on the older models. High amperage overload: The first thing to check is to see that there is adequate air flow through the condenser coil, see if the fan running or could dust be blocking the coils. To test for overload connect a 10 amp scale ammeter in series with the power wire to the module and watch the start up and running amps. If the start amps exceed 9 amps or the running amps are above 7 amps, there is an overload. An amperage overload indicates the compressor is faulty or if recently serviced with refrigerant there is a refrigerant problem.
