I have one air conditioner unit, China one, which was installed in 2004. So, far when it cannot flow cold air, I ask my technician to check for freon leakage.
But, now I am in doubt? Can you recommend me how many year can I used that unit?
As long as it's running or can be fixed economically it can be used. 20 to 25 years is usually the intended lifespan of a large a/c unit. I don't know about smaller window units. I suspect they don't have as long a service life and the cost of fixing them could cost as much as a new unit. Until a technician inspects the unit, you probably won't know if it's worth fixing.
Old window units (like old appliances) were built to last. New units (both categories) will not last because they are not designed to. The cheapest windiw units may not cool half as good as new when just 2-3 years old; the mid-range ones can usually go 5-7 years before replacement. Nothing like the 20 year old unit in my Mom's window which has never needed anything except annual visual inspection and cleaning.
Just the way the world is today!
Phil is so right about this.
I have a rental with an old Fedders wall a/c (at least 50 years old) - still running every time the CENTRAL A/C ( about 10 years old) breaks down.
All appliances, with no exception, are designed to break down faster than ever. It's called "renewable business" for the manufacturers.
My 1924 house had a working a/c that was 35 years old. It was expensive to run.
Modern HVAC systems are much more efficient...my new a/c uses considerably less electric. Note: the new furnace also improved the new a/c efficiency.