If your AC is turning on fine, but is only blowing hot air, then you probably need to replace the capacitor in your outside unit. To double-check further, turn your AC on, then go outside and look at your outside unit - it should either be not working at all or making a "buzzing" noise - like it's trying to start, but not starting.

Replacing your capacitor is about as hard as replacing your car battery - you can easily do it yourself and save yourself a few $ hundred in labor.

Here is the step-by-step video on how you can replace your capacitor. You do not need to diagnose anything - just replace the capacitor.

IMPORTANT - Make sure to disconnect the power next to your outside unit before working on it. It will either be a breaker or a plug that you physically remove.

To find out what capacitor you need, either look up the model of your outside unit in Google and it will tell you, or open the outside unit up and look at the capacitor. You need to buy a new capacitor that has the same specs (capacitor size does not matter).

I recommend buying several capacitors in advance on Amazon (they are around $15) and having them ready in case you need them. But if your AC breaks down in the middle of the summer and you need a new capacitor right away, buy one from an HVAC supply place. They may charge you double there since you do not have an HVAC license, but it will still be way cheaper than hiring an HVAC tech.