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Hello I will help you with your question,
If you cannot communicate directly with the HVAC control module with a Tech 2 start at the class 2 data list and scan for codes. Post any codes you get here and I will help you work through the diagnosis. You can also ping the modules and watch the right column to see which do not respond.
Is this an auto or manual system?
And did you check the class 2 data bus for codes and ping the modules to see which are active on the data bus?
You will need a diagnosis and with the scantool it is possible to see the communication lines. Were there codes?
Could you communicate with the other modules? ABS, PCM BCM etc?
This was a Tech 2 scantool?
Were any codes set?
OK this is an advanced diagnosis and for communication issues you have to have a Tech 2 to see the class 2 data buss and how the diagnosis proceeds is dependent on the data and codes that the scantool displays so doing it second hand is almost impossible.
You did the "throw a part at it and see if it sticks" routine so if the control head you installed is OK then the data buss or power and ground is the next issue but the codes that set in the other modules will show what is happening so it is critical to have all the codes and data.
Sorry there is no silver bullet for an issue like this
Let me know if there is anything I can do for you in the future