Hi Jamie,

I’m surprised you measure 24 volt. When I did the same I measured exactly half the voltage of the 24 volt system (about 13 volts when you are on shore power).
Did you measure under load? The whole Frigoboat system is made up in such a way it does not matter if your ships system is 12 or 24 volt. The compressor also reduces the actual supply voltage of the compressor motor to 12 volt irrespectively of the power-supply.

I recommend you check it once more. Maybe use a lightbulb to make up some load. If you still measure 24 Volt your switchbox may be broken, also explaining you extreme short lifespan of the pump. 

Regards,

Arno Luijten
SV Luna,
A54-121