Edit: typed on the iPhone after a big day. Please forgive any grammatical errors, until I get access to a pc to clean it up, lol.
A system "service" is a gimmick. An ac system is fully sealed. If your losing refrigerant, it's because of a system leak. There are many other factors to consider, aside from a "leak" also, such as air flow, and heat transfer, as an air conditioning system is all about transferring heat, and reducing humidity.
If your ac is "on the way out" I'd suggest a few simple checks yourself before you take it to a dealer/shop.
Wash your condenser. The big finned core assembly infront of your radiator. Reduced airflow through this causes higher head pressures, thus reducing heat exchange efficiency, especially in stop - go traffic. Wash this with gentle running water, normal hose pressure with a nozzle is fine, any more pressure, and you risk bending fins. If your ac runs cooler whilst your driving at speed, than when your slow/stationary that would be my first port of call, as well as making sure your thermo fans are operational.
Check your air flow at your vents. If your airflow isn't what it used to be, or you drive around with your ac on fresh air, as opposed to recirculate, then chances are, your evaporator core has a coating of dust, which when wet turns to mud, and reduces airflow, thus again reducing cooling efficiency. Smokers, I'm looking at you for this one.
Make a visual inspection of your ac system. Look at your compressor, condenser, reciever drier, and any joins or fittings. Any oily residue you can see is a surefire sign of a refrigerant leak. Whilst this isn't easily repairable by the average guy, it will give you an idea of what to expect from the shop you take it too.
Don't forget the obvious! Does your compressor have a belt on it? Is the belt tight? An average ac compressor needs approx 10hp to work at optimum level whilst under load, and requires belt condition accordingly.
The front if your ac compressor is likely a two piece unit. You should be able to manually spin the front section of the pulley by hand without too much effort, If not, you may be up for a new compressor.
Do you have ANY refrigerant if your system? Along your ac lines there will be two fitting receptacles, or service ports. Inside those are a Schroeder Valve. Same as on your tyre valve stems. Briefly press on one of the pins on those valves, and refrigerant should escape, as these are your ac system access points. This isn't technically legal, mind you, so I have to advise against it. But it will tell you if you have any refrigerant at all. If you have zero refrigerant, and you cannot spot any leaks under your bonnet, then prepare to open your wallet, as you have a leak in your evaporator core assembly.
When your system has been running for a while, 5 minutes or so, place a hand in the larger of the two pipes on your compressor. This is your return line, or suction/low pressure line. This is the pipe that returns from your evaporator. This pipe should be cool to the touch, and noticeably cooler than the smaller if the two, your discharge line. This one will be uncomfortably hot to the touch on a correctly operating system.
Whilst these observations are not specific to the vt/x series of commodores, especially those with variable displacement compressors, hopefully it can give you guys and insight as to what is wrong with your air con, BEFORE you hit a workshop. Remember however, that to legally do any repairs, you must be licensed by arctik, the governing body for those with qualifications in the field.
Nothing can outweigh the ability of an experienced technician, with the correct tooling, so use thus information as a guide only.
Hope this extends your vehicular knowledge!
Jako
im gonna go ova a few of those thigns you mentioned, i mainly asked so i have a heads up in the future, but i deffinitly got more then i asked for, and im more then happy 