The answer to 'air filter blowing hot air' is that a clogged or dirty air filter is the most common cause. A dirty filter restricts airflow, forcing the HVAC system to work harder and blow warmer air. This can also lead to higher energy bills and potential damage to the HVAC components.
To fix this, the first step is to check and replace the air filter. Depending on your system and usage, air filters should be changed every 1-3 months. If the filter is very dirty or clogged, replace it with a new one. Make sure to choose the correct size and type of filter for your HVAC unit.