I just checked again and under load (with my new 12V pump) the pump output from the Frigoboat interface is clearly showing 24 volts, and the 24V light is on, just as in Scott's photo. It is as Scott indicated 25 or so volts - not 12v.
Somehow the interface is converting the compressor output BACK to 24 volts. I looked at the schematic, but it is a bit sketchy and not very detailed.
I got the 12-volt pump to run, but to get it running I had to replace the interface fuse with a 5 amp fuse. It is supposed to be 2 amp, and I have always needed a 3 amp. Now a 5 amp - wow??
I see the interface flashing "pump overload" every 5 minutes or so, and the pump is running very hot. That is likely because it is running at twice the speed.
I am working the brushless motor deal and have a question for Oliver. I got it working, but still have not tried the motor itself, as it has to be bolted down first. I am sure I can get a solution there.
In the meantime, at least I have refrigeration for now. The new Flojet is thermally protected, so I am pretty confident it will not burn up right away. One alternative might be to use a relay interface or DC converter that will in fact deliver 12 volts to the pump from another source in the engine room. We could use the interface pump output to drive the relay only.
Dazed and confused as always?
We have to come up with a solution here that can be replicated.
Phantom, A54 #44