My AC worked great last summer. After I had some work done in December, my AC doesn't work. I just blows out hot air. I had some kind of rod fixed and the exhaust fixed. Could they have done something to cause my AC not to work? Also, after the work was done, I now need to have an alignment. My steering wheel is not straight. Should that have happened?

Probably replaced a tie rod - which should be immediately followed by an alignment. If you don't get an alignment, you get excessive tire wear and pulling. Exhaust won't affect AC.

I believe when air outside is below a certain temp, the A/C will not kick in. It'* possible that they may have unplugged something while they were doing the work.

Replacing a tie rod and some exhaust work will not affect your A/C. It maybe be because it'* cold outside (depending on your location), or it may need to be charged.