Isotherm self pumping compressor wiring question - strange realy set up

[mitchc]

Whilst replacing the toilet and associated plumbing in our aft head, I took the time to access the fridge & freezer compressors (via a hatch in the aft head into the galley).

They are (i think) original Isotherm self pumping compressor - the new versions are here https://www.indelwebastomarine.com/u...ature-control/
At the moment both compressors are switched by a single breaker at the main panel. We'd like to be able to switch of either the fridge or freezer independently to allow for cleaning/maintenance as required.
This is a relatively simple change to the wiring which I'm happy to do.

But whilst doing this change, I've found an external automotive type relay that is connected to the compressor control box via a screw into the side of the box. It's connections are
Pin 30 - +ve from the main breaker
Pin 87 - -ve
Pin 85 - connected to compressor control box screw with green/yellow wire
Pin 86 - -ve and to pin 85 via a diode.

I can find no reference to this external relay in the manual we have on board or any I can find online.

Any thoughts on what it does - at the moment it seems if it does energise, it will connect the 24v +ve supply straight to ground


Thanks in advance...

 

[PaulRainbow]

85 and 86 are the coil terminals, so where does the green/yellow wire go ? Does it connect internally to something in the control box ? Either way, if the relay closes it will indeed short the +ve to -ve. If you unplug the relay does the compressor work as normal (i suspect it does and the relay is superfluous).

 

[mitchc]

85 and 86 are the coil terminals, so where does the green/yellow wire go ? Does it connect internally to something in the control box ? Either way, if the relay closes it will indeed short the +ve to -ve. If you unplug the relay does the compressor work as normal (i suspect it does and the relay is superfluous).

That was my thought exactly - next task is to take the control box apart to check what it's connected to.
But other than that it's going to be removed as it seems to have no function....unless I get any other responses on a couple of other forums I posted this question.
There is the same relay set up on both the fridge & freezer compressors, so it was obvioulsy thought neccesary when they were installed......

 

[PaulRainbow]

That was my thought exactly - next task is to take the control box apart to check what it's connected to.
But other than that it's going to be removed as it seems to have no function....unless I get any other responses on a couple of other forums I posted this question.
There is the same relay set up on both the fridge & freezer compressors, so it was obvioulsy thought neccesary when they were installed......

Hard to say for sure, but it was possibly there originally to have heavy wires to the relay and lighter wires to the switch panel. Things tend to get changed over the years and who knows what some of the redundant stuff was for.

 

[mitchc]

So to close this out - I managed to find the original manufacturers of the compressor system who are based in Sweden.
Very helpful, but confirmed the extra relays were not by them.....

The circuit board in the control box is fully potted so can't really see what is going on with the circuits, but the screw the green wire attaches to just seems to mount the control box to the compressor.
I figure the relay was added as some kind of "earth protection" circuit, but all it would do is trip the main refrigeration breaker if it ever energised.
Anyway, I've removed the relay and associated wiring and the fridge/freezer are working as normal so I think it's a win for the "remove excess wiring and complexity from the boat" project.
thanks for the input Paul.