The coolant loss could be caused by a defective reservoir cap, or possibly a pin hole leak in the plastic tank. Both are common, though 1/2 liter in two days is excessive. It's also possible that you have a small radiator leak.

Regarding the AC, your symptoms are consistent with low freon. A '93 model which has not been recharged or repaired is unusual. Most people start off with the recharge approach (<$100), and do the expensive evaporator replacement if it doesn't hold satisfactorily (>$1000).