The answer to 'air conditioner not heating' is that the most common causes are a malfunctioning heating element, thermostat issues, or a problem with the refrigerant system. Symptoms may include the unit blowing cool air instead of warm, the heating not turning on at all, or the air not getting warm enough.
Some potential solutions are checking the thermostat settings, replacing the heating element if it's faulty, or recharging the refrigerant. However, these repairs often require the expertise of a professional HVAC technician, especially when dealing with the refrigerant system. It's best to call in a pro unless you have extensive HVAC experience.