The answer to 'AC blowing hot air' is that there are several common causes, including a refrigerant leak, a problem with the compressor, or a blocked or dirty air filter. Symptoms include warm air coming from the vents, the AC running constantly, and high energy bills. Solutions can range from simple DIY fixes to calling in a professional HVAC technician, depending on the root cause.
If the air filter is dirty, you can try changing it yourself. But if the problem is a refrigerant leak or an issue with the compressor, it's best to call in a licensed HVAC technician to diagnose and repair the problem. Attempting to recharge the refrigerant or work on the compressor yourself can be dangerous and may even void your warranty.