If it’s blowing hot like the heat is on, not just room temperature, then most likely your blend door actuator is not moving. To confirm, move the controls slowly back and forth between hot and cold. You should hear the blend door moving inside the dash. If not, that confirms the problem. If you have a scan tool with bidirectional controls, you could use that, instead.

There are multiple possible causes for a blend door that is stuck on heat, including a faulty actuator motor, fauty control head, or a wiring issue. If you have an automatic climate control system, a faulty temperature sensor or electronic control unit are also possibilities.

If the blend door does move all the way to cold, and the air is room temperature, not hot, then the problem is in the cooling system. There are quite a few possible causes of cooling system problems. Try searching for how to diagnose car air conditioning not cooling. A good scan tool will help in diagnosing cooling problems, as will a set of pressure gauges. If you’re in the USA, you should be able to borrow AC gauges from a local parts store.

If the compressor comes on, does the line going in get cold? If it does, then probably a blend door in dash.

All the advice mentioned is solid advice. But Another way to tell if blend door or an actual AC problem. Look for water dripping on the ground after you run the AC for a while. Should see water dripping behind passenger side tire somewhere.

If no water. It’s not cold enough to condensate.

Just because a compressor comes on doesn’t mean it actually has Freon in it, if you may just be air pressure which in turn will turn the compressor on. Does the low side line get cold and sweaty if yes it could be blend door, if no it’s probably out of Freon and just air pressure in system vacuum and recharge system.