Marine Air A/C blows breaker instantly

[golgi]

On my new-to-me 2001 Carver 530, my master stateroom air conditioning doesn't work. Salon, VIP, and Pilothouse Marine Air units are working great but the breaker to the master unit blows instantly. I've replaced the breaker assuming that had gone bad, but same result. I've checked, cleaned, and reinstalled ground on the unit. I've removed the ducts and reached inside and the cage spins freely. I cleaned all the grounds on the small buss bar in front of the port motor. Same result. Breaker flips immediately. Short in the motor? I'm at a loss. Any help in tracking down the culprit would be greatly appreciated!!!

[waybomb]

Blowing instantly, meaning, as soon as you flip the breaker before turning on the ac unit?

I''d start with disconnecting and protecting the termination at the ac unit, and flipping the breaker. Just to make sure the line between the breaker and the unit hasn't been compromised.

[golgi]

Source of the post Blowing instantly, meaning, as soon as you flip the breaker before turning on the ac unit?

Yes, exactly. No chance to even turn it on at the A/C control unit. Breaker pops as quick as you can flip it on. Unplugged the phone-like jack from the control panel to make sure it wasn't causing the problem. Same result.

I will disconnect the wires from the A/C unit next and see if that makes a difference at the breaker. Thanks for the suggestion.

[waybomb]

Not knowing your ac unit, if the problem isn't the line, then could be a bad termination board, or a short to ground at that board.
Just make sure you unplug your shore power before playing with ac on a boat

[golgi]

Isolated the wires at the unit and it didn't make a difference with the breaker. Traced wiring back and recleaned all the grounds. No difference. Removed the control board cover in the engine room. Everything looked good... No char or signs problems. Tightened down the screws. No difference. Should have read your response first. I took 220v from about the 8th screw I tightened up. That woke me up better than my coffee this morning...

So bad board possibly?

[waybomb]

If the ac unit is disconnected from the line, then the only things it can be is the breaker and the wire. If there are more connections in between the load and the breaker, keep going back and disconnecting things until the issue goes away.

[bud37]

You can check for a short by continuity testing with no power on .....all you have to do is isolate each leg of the circuit to be tested then test across the wires where there should be no circuit....if you get continuity then there is your short.

Do this with all power off....that means shore and any inverters you may have. FYI I have had wiring get a small cut and rub against a receptacle housing and cause just what you are seeing.

[golgi]

Thanks for the help guys!! Truly appreciate it

Unfortunately, I had to return to the real world so I'll get into it again this weekend. My circuit goes from breaker to control board to A/C unit. I think I'll kill the power and inspect and reinstall all leads and grounds on the board and then go from there. The wires are jacketed, insulated and then inside flexible conduit. I can't imagine I've got a rub through but who knows. Like you said bud, maybe inside a junction box. When I test for dead short would I just run a lead wire from the connection in the master to the engine room? The multimeter isn't gonna cover that distance

I consider myself good at many things, but the dark magic of electricity is not one of them!! Lol

[bud37]

If you are saying it may be in the feed cable from the breaker to the AC unit.....just disconnect both ends and check across the wires.......imagine a 2ft three wire cable laying on the bench with the wires exposed at the ends....you test no cont. from the white to the green, which is correct.. now touch the white and green together at the other end and you will get continuity and so forth...that is the picture to go forward with......anywhere along that cable could be the sharp end of a screw etc .In my case it appeared to be a defect from the factory that finally wore thru(.right where the cable sheathing was cut)

I have a 20ft piece of wire with alligator clips to help with testing from one area to another....good luck man, take your time be safe and you will find it.

[golgi]

Ok so I finally figured out out. The windings in the compressor had grounded out. When I disconnected the unit in the master, that was not the culprit. It wasn't until it dawned on me that it had a remote compressor that I disconnected that in the engine room and the breaker did not pop. Tested the system for leaks and it held 205 psi of nitrogen for several days so just going to replace the compressor rather than replace the whole setup with a stand alone unit. Looking forward to some a/c in the master, although with this summer we haven't really needed it too much!