My ac unit is acting up, I think it's low on freon. I borrowed a friends gauges and vacuum pump, just not 100% what to do. I'm guessing I'll hook up to the low press and high pressure fittings and see if I have any pressure. If none then hook up the vacuum pump and see if she holds pressure, then check for a leak if need be?

What model and what is it doing? I had a cruisair unit once that gave me low freon codes on the display but turned out it was a bad control board. Go figure

I have some spare ac parts also you could try. What model? Can you post some pics?

Ocean marine which I believe is out of business. It did show a hpf code at first so I replace the switch and it worked for a while. Then it came on again so I wired it out of the switch and it worked fine for a while. Later the lpf came across the screen and that was last fall. It's doing the same thing this spring. I don't think the ac was use much before me, and I'm guessing was prob low on freon.

Model is SCL5012.OR
12,000 BTU

I hooked up gauges yesterday and have 0 pressure on high and low side. Hooked up a vacuum pump and let it run for about 30 mins and the system would not hold the pressure when I closed the valves. Took about 5 mins to lose all the pressure. I might try and check for a leak but I'm gonna need some R22.

Check all of the piping and components for oil residue. If the Freon leaked so did some oil .if you have access to a nitrogen tank and regulator pressurize the system to 200 psi. and use dish soap to look for leaks. if you find the leak it must be brazed do not try to solder it like plumbing it will fail there is too much vibration in a boat. pull a vacuum for at least an hour. use digital scales and weigh in the refrigerant charge, don't guess. the amount is found on the tag with model no. also look for cracked tubing.
feel free to call me been doing this almost 40 yrs.
chris 214 309 8081

I do have access to nitrogen do pressurize the system from the high side or low.

And what is brazing.

Pressurize both sides. start low maybe 50 psi if you can't find it then increase the pressure. Brazing is a high temp type of soldering most guys use a brazing rod containing 15 percent silver content. If you can't do it take it and have it done. As I said before there is too much vibration in a boat to use regular solder and much higher pressures. But it may just be a loose fitting somewhere.

those units were not very good from the start, had dealings with them...you may be able to patch it up for a while, the coils were made super cheap and failed quickly, I have sold several people mermaids that had those and complained about them failing after only 2-3 seasons...feel free to contact me if I can help out...Rob