First, I feel your pain. I'm in Houston at my girlfriend's place; we live in a single family house, and the A/C is running all day even with the thermostat at 84 degrees. I work from home, so I can't let it go up higher than that. Our outside thermometer recorded 106 degrees today.
The things that we've added to the house to help keep cool, besides new insulation and having the A/C unit checked, include a bunch of things. First, a little theory. Your apartment heats up because of the sun heating the building primarily, and secondarily because of infiltration from the outside of warm air.
I'm going to just assume that your landlord isn't willing to replace your windows and doors with low-E dual-paned units. I've done this to my house in Bryan, TX and it literally cut my utility bill in half.
The first thing we did with her place, where the landlord is also not willing to rip out a ton of windows and replace them, was to get blinds with reflective shades in all of the windows, and external solar shades or screens where possible. Remember: Black stuff is OK on the outside of the structure, because black absorbs heat (and you don't care about the heat if it's on the outside) -- and white things on the inside of the structure, because you want the heat to not be absorbed and to just be reflected back out.
The second thing we did was to get a better thermostat for the house. The old one was a manual one with mercury in it; the new one has a digital timer and a bunch of other features that include breaks for things like the compressor coils to defrost.
The third thing we did was start replacing the A/C filter frequently... at least once a month.
It might help to suggest more if we knew what kind of A/C unit you have (is it one of those high-rise below-window units, or a 'real' one with a compressor and air exchanger in a closet or attic?), and what kind of structure (concrete or wood frame) you're in.
I'm in Michigan and we get harsh winters and salt our roads. Salty roads and ice get on our cars, and this combination is really harsh on our metal parts of our cars. Salty humidity is also very harsh on any metal parts, even galvanized steel. Now galvanized steel in the US has improved in the past 20 years, but it is not impervious to salt water.
That said, you will need to have all important parts coated some how to prevent corrosion as salty humidity is super corrosive. There is a service in the US that coats cell phones with a nano coating. They don't even take apart the cell phone. After the phone is processed you can drop it in a pool and it will still work. The phone is guaranteed for life vs moisture and water. Liquipel.
If the AC company has this service available they can coat their PCB boards and that should help a lot. Or they can use another coating on the PCB boards. The coating cannot conduct electricity or it will short out the boards.
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The neoprene foam is what I use on the line set , it is easier to shape and a small tube of neoprene glue you can make custom sizes quite easily. The foam stuff is cheap but hard to shape.