I have an 06 Silverado 1500 with over 200K miles. I just picked it up from the shop yesterday and immediately drove for two hours. I get close to home and realize I can't turn the air down, the indicator shows that I dialed it down but its still at top speed. I get home and turn the car off and the fan stays on. I take the key out fan stays on. Called the mechanic he told me to unhook the battery for now and bring it back in on Friday.

Two questions. What's wrong and can I fix it myself?

My second and more important question: The truck was in the shop because the seats, seat heat, and right side door locks and windows stopped working. He fixed that, said it was a short of some kind. Is there any chance the mechanic did something inadvertently to cause this or is it just a coincidence?

Thanks!