My auto scanne is not able to read my trucks computer. It reads that a vehicle must be plugged in which it was. It is not the scanner because I tested that. The battery was replaced and the a.c. Did not work properly. I disconnected the battery to reset the a.c. And the engine light came on. Did I fry the computer?

I'm not sure what is going on. The ECM may have taken a hit. Did you turn the ignition switch to ON, while you had the scanner plugged in? Have you tested all under hood and under dash fuses with a test light or multimeter?