I don't think you would get any codes.
The Tech 2 would allow you to dive deep into the HVAC to see what various parts are doing (or not doing).
You should be able to look at things like expected and actual input/output voltages, command things to turn on/off or open/close and see what the response is (or isn't).
The control of the different components and being able to watch what they are doing, is the value of having the Tech 2 (or other bi-directional) scan tool.
While other bi-directional scan tools (like Autel, etc.) are awesome and do have abilities to command things and test many component functions, the Tech 2 is what would be needed if components needed to be programmed (ECM, BCM, radios, etc.).