The answer to 'why is my air conditioner not heating' is that your air conditioner is not designed to heat your home. Air conditioners are cooling systems that remove heat from the indoor air and transfer it outside. If you need heating for your home, you likely need a separate heating system, such as a furnace, heat pump, or space heaters.
Common reasons why an air conditioner may not be providing heat include a malfunctioning thermostat, issues with the compressor or other internal components, or problems with the electrical connections. In some cases, the air conditioner may be the wrong size for your home, leading to insufficient heating capacity.