10 years
Monthly.
5yrs
once a month
Freon (or any refrigerant) only needs to be replaced if it is low. You can have the refrigerant checked at most auto repair shops and they can tell you if it's low. If it is, they should also check for leaks as it is a closed system and does not normally lose refrigerant.
Never! If it's low on refrigerant it has leaked.
every 12-18 months
at least annually
I've been driving my 1995 Ford Explorer for almost 14 years and have never had to add refrigerant - the system still works fine
Once every 6-8 months.
Recovery from spine surgery is a long and often painful process. Your doctor will prescribe physical therapy to help speed your recovery. Be sure and follow that regimen carefully for the fastest recovery.
Never, unless you suspect of not cooling then there is a leak somewhere. A repair will need to be performed before recharging.
You local Governement Aviation Authority should have the standard required