l have a 1987 Porsche 924s that had been stored for 18 years, and l currently drive it like once a week(it only has 20000 miles on it). One day l started the AC, but it worked perfectly, but somewhat loud. The problem is that sometimes the AC starts at an extremely low setting with it off.Usually there is a slight electrical sound like the ac barely starting then a faint constent cold air comes out of the vent. How can l stop it from doing this please.

Storing the car was very bad for it. The AC system is probably corroded inside, and will need to be rebuilt ($$$$), it may be cheaper to completely replace.

On another item - hopefully and drained and flushed all the other fluids (coolant, engine oil, transmission, rear end, brakes, steering) before driving it after storage.