GBM, 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 at http://www.kollmann-marine.com. There are several sections
on all these compressors also 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 even it compressor is running on 24 volts, 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 is
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, when operated on 12
volts, there is an overload. An amperage overload indicates the
compressor is faulty or if recently serviced with refrigerant there is
a refrigerant problem.

The module is more likely to fail than the Compressor but WARNING, do
not install a new module on a compressor that test bad with the ohm
meter.