AC Pump Trips Main Breaker

When you say “turn on the AC breaker” do you have only one breaker for the entire system or have a separate breaker for the pump and each air con unit?

does your pump run at all times or does it only come on when a compressor comes on?

reason I m asking is that there is usually a delay between the when an air con breaker is turned on and when the unit calls for the pump to start. So if the pump breaker trips right away, the problem could be with the relay box so before replacing the pump you may want to disconnect it and see if the breaker still trips.

that said if the pump is actually 17 years old, it would be a record. The oberdorfers usually fail every few years from impeller or head erosion

you may want to relocate the new pump to a better location

Pump controllers have the potential to fail and trip the breaker. They usually just die and not work.
Looks like a sky-hook would help, support the tables and remove the legs to get to that pump.
Try to turn the motor shaft before complete removal, could just be stuck and not spinning up.

Probably the best advice.
Find a better synthetic pump. Spend the bux now and sleep well for a long (long) time.

Ok don’t sounds like you have a relay box aka triggers aka triacs

if none of the units have the compressor running, only the fans then the pump will be off and will NOT have power. There is usually a delay for the air con control to initialize so with all the breakers off, the pump will not get power instantly. If the breaker trips right away, it’s likely the wiring or the relay box. Disconnect the pump in the relay box, should be a cruisair box near the condensers and see what happens.

and/or bypass the box and power the pump directly as a test.

Replacing just about anything is always a good advice, but by the same token, the OP could as well replace the whole boat with a brand new one...
I mean, just to name another possible culprit, I've seen shorepower tripping due to a bust capacitor, which is worth 20 bucks or so.
I'd want at least to check all the "easy" possibilities, before using the checkbook to fix the problem!

It could be the in the box or it could be wiring.

with the air con units off, the pump should not be getting power so it shouldn’t trip its breaker.

easy to check: disconnect the two wires going to the pump (lower right) and see if the breaker still trips.

With a 230 Vac unit, one of the legs (L2) to the motor is always hot (those two white wires). The other leg (L1) is switched by the triac, that lil thing with the yellow wire to it on the right.
If you pull one of those white wires and the breaker does not trip, bad motor or bad wire to the motor after this box.

The triacs only run one leg on a 230v system? That s crazy

Yes, Also one of the pump trigger lines from the controller (L2) is always hot. Same with a 230Vac blower fan.

In a 115Vac config, it (L2) would be neutral and not surprise you & curl you hair.

One last hope, Re-connect the white wire in the pump controller box. Disconnect the white wire form the motor. Check breaker.
If it does not trip, carefully inspect the white wire for chafe around the pump.
If you don't find anything, then as the norm, and has been mentioned, the OLD pump has screwed da pouch for its last time.

You can dig into the motor deeper your self, send the motor to a shop and then, have a patched motor with aging bronze pump body OR replace it with a whole composite assembly and sleep well for a very long time.

I'm not familiar with Oberdorfer raw water pumps because they are unheard of, around here.
But if that's what their lifespan is supposed to be, the last thing I would do is replace one with another cr@p product from the same manufacturer.
I've got original Gianneschi and Calpeda raw water pumps in my 2004 boat that still run flawlessly, and I can say the same of other similar ones I've seeen in 30+ years old boats!