The answer to 'AC not heating' is that there are several common causes, including a malfunctioning thermostat, issues with the heating element or compressor, low refrigerant levels, or problems with the electrical system. Symptoms can include the AC blowing cool air instead of warm, the system not turning on at all, or the unit short-cycling (turning on and off rapidly).
In many cases, the solution may be as simple as replacing the thermostat batteries or cleaning the condenser coils. However, more complex issues like a faulty compressor or refrigerant leak will likely require the expertise of a professional HVAC technician. It's generally best to call in an expert if you're not comfortable troubleshooting the system yourself, as improper repairs can lead to further damage or safety hazards.