Don't let anyone check your auto A/C as a maint. or "A/C tune-up". If it's working --let it be. Simply use it.
Attaching "hook-ups" to your car can sometimes disturb the seal components of your AC connectors introducing a new leak to your A/C system. Again, if it's cooling....let it be.
The only maintenance (if A/C is working fine) would be if your vehicle model came equipped with a CABIN AIR FILTER. This interior filter will restrict circulation of your inside air if dirty or clogged. Generally the cost is around $40 to $50 installed and requiring replacement about once a year depending upon use.
