Moved my filter to the garage

Its the airhandler, i knew it was to good to be true...i will move it around, i think i know were you going with it, saltwater vapors will rust it out? how far away should it be?
I mostly go to house of fins, the ac unit i have is for a much bigger house, so i set to around 76, but it feals like 70, and since the thermostat is upstairs, the house is always warmer upstairs, so by the time it gets to around 76 downstairs is like a walk in cooler.