Correct. With the exception of USA cars (GM, FORD, etc.) which use a J1850 bus. On those vehicles there's a good chance the A/C is on the standard pin.
For BMW the A/C is on pin 8, not 7.
When the vehicle has Can-bus, the A/C is NOT on the high-speed bus supported by the Elm-interface. It's on the mid-speed or low-speed can-bus which can be connected anywhere in the diagnostic socket.
There are some good affordable programs for a couple of makes.
For VW/Audi/Skoda/Seat and the Ford Galaxy use VCDS (Used to be called Vag-com).
www.ross-tech.com
For Opel/Vauxhall use Op-com. Will work on some Saab's too.
http://www.vezerdiagnosztika.hu/index_en.html
For Bmw use the bavarian Technic:
http://www.bavariantechnic.com/
For Porsche use durametric:
http://www.durametric.com