A/C and Heating

Looking for recommendation for A/C and heating service repair. I have had a handful of different companies and local people come out and tell me a handful of different problems. Just don't know who to trust when one says I need a new unit and another says I need one thing replaced. Very hard to find someone on weekends, which is the only time I'm home for more than an hour at a time to assist and direct to issue! Not afraid to try and fix myself, I just want to avoid taking out coil and breaking other parts of machine if they're still good! Please HELP!