Oil-pressure switch keeps giving out

[Akka]

We have an engine-driven refrigeration system (we have a 12V system in parallel, but that's another story). The compressor clutch excitation line runs through a manual switch and an oil-pressure switch, in series. That way, the clutch circuit is disabled whenever we want it to be or when the engine isn't running.

We live aboard, almost always at sea or at anchor, and use the engine-driven fridge system almost daily. The oil pressure switch gives out regularly. Not every month, but more often than once a year.

We actually have three oil-pressure switches aboard, one for each alternator and the one for the fridge. The two alternator switches have worked fine for decades, without replacement. Any idea why the compressor clutch circuit is different? The only thing I can think of is current -- the other two circuits are sensing only, no real load.

And what is the solution? These switches are hard to find, at least in the more developed parts of the world. They have two poles and screw into an oil pressure manifold. It turns out (I have a lot of experience with this) that there are two thread pitches. Ours is more common, and in some places (Morocco, Panama) our switch is widely available -- just walk into 3 or 4 little family-run stores and ask for one, and one of the stores will have it. I can't find them at all in the US, having visited just about every chain auto parts store there is (Napa, CarQuest, Pep Boy etc.). Of course, I'm hampered by not having a car model to give the clerk -- amazingly, none of their databases can be searched by part type. But eventually the clerk goes back into the shelving and looks for anything that appears to be similar to the old switch I've brought along. This is the one quest I've found easier to carry out in Spanish or French than English!

Anyway, suggestions are welcome. Meanwhile, I can simply short across the switch and we have to remember to turn the fridge off manually. Otherwise, we'll burn the clutch out in short order (been there, done that).

[meridian28]

You may want to try a small relay. An auto parts store would have the kind that are used for a starter motor.

[Akka]

Thanks, Meridian!

[Cheechako]

Are you talking about a switch for engine oil pressure that disconnects the refridge if low pressure? Do you have a low pressure alarm on the engine? IF so why not eliminate the various pressure switches?

[donradcliffe]

Originally Posted by meridian28

You may want to try a small relay. An auto parts store would have the kind that are used for a starter motor.

+1 ---you have too much current going through the switch.

[a64pilot]

If I was going to the auto store, I'd get a relay for the airconditioner clutch, not the big starter one

[MBWhite]

I agree with the above posters.

Additionally, I would ask for a "Bosch Style" or "Ice Cube Style" relay:



These things are universal all over the world. They are a universal style so if you get one from a different manufacturer I wouldn't worry about it. Also get a "Relay Harness"


So you can swap out relays if one ever goes bad. I'd get a spare to have on hand as they are only a couple dollars. Actually, I'd get as spare harness too and then you not only have spares but you can always use it for a completely separate application too if needed at some point.

[rwidman]

Originally Posted by meridian28

You may want to try a small relay. An auto parts store would have the kind that are used for a starter motor.

Yes. I suspect you are attempting to switch too much current through the oil pressure switch. I doubt you would need a starter motor relay. You can get relays at auto parts stores that are rated for extra driving lights or horns. These should be rated for 20 amps or so and have the same spade terminals often found on boat wiring and a mounting leg.

I use one to power my depth sounder so I can leave the GPS (and anchor alarm) on overnight without the additional current draw of the depth sounder.