Refrigerant changes from gaseous to liquid in the compression process and is circulating in the system at pressure. Leakage through openings is lower as a result.
When there is no liquid in the system, the gaseous material is gradually let out through the openings. These don't have to be visible - think of it as very slow permeation.
Even then, two years sounds pretty drastic. We lost a lot of pressure in our AC four years after shifting it from a different floor. On the original floor, the AC had run for ten years and it has lost zero pressure. Like you, we only use AC during summers and this AC hasn't been used in three summers.
When there is no liquid in the system, the gaseous material is gradually let out through the openings. These don't have to be visible - think of it as very slow permeation.
Even then, two years sounds pretty drastic. We lost a lot of pressure in our AC four years after shifting it from a different floor. On the original floor, the AC had run for ten years and it has lost zero pressure. Like you, we only use AC during summers and this AC hasn't been used in three summers.
