Fridge compressor - drawing current without running

[MattS]

Either low battery or too thin cable if running the engine i.e. charging, gets it going. You didn't say this before!

No sorry not specifically - but in OP I did say that cutting the 12V and re-enabling seems to snap it out of it - and that happens with or without the engine running I found.

And would low voltage supply explain why it would drawing significant current without actually running the compressor?

 

[Refueler]

Some of these 'DC' fridges are something a bit like a 3-phase AC motor driven by a bunch of electronics.
No brushes, just 3 connections going to the sealed motor/compressor unit.
Could be the electronics failed, a bad connection, or the compressor jammed.

I assume the boat hasn't been laid on its side, fridges don't like that!

Many items today are changing to Brushless (which you have described) replacing the old brushed motors. More efficient, higher power size for size ... and less to wear out ...

 

[vas]

if you download the Danfoss manual for these compressor fridges (iirc BD35) you'll see that in the control module there's a D terminal (again iirc) it explains how to wire a 5mm red led on that (and GND) and the flashes it comes up with explain what's going on. When I had issues with my batteries, I installed that on both fridges so I knew exactly what was going on. Well worth diy addition imho!