The answer to 'air filter blowing hot air' is that a dirty or clogged air filter is the most common cause. A dirty filter restricts airflow, causing the air to heat up as it passes through the system. This can lead to the air blowing hot, rather than the expected cool air.
Other potential causes include a malfunctioning blower motor, a problem with the thermostat, or issues with the refrigerant levels. If the air filter is clean and the issue persists, it's best to call in a professional HVAC technician to diagnose and repair the problem.