The answer to 'why is my thermostat blowing hot air' is that your HVAC system is likely stuck in heating mode, even though you want it to be cooling. This could be due to a thermostat malfunction, a problem with the HVAC system controls, or an issue with the cooling components.
Some common causes include a thermostat that is set to 'heat' instead of 'cool', a faulty thermostat, or a problem with the HVAC system's compressor or refrigerant levels. In some cases, the issue could be as simple as a clogged air filter or a problem with the electrical connections. If the problem persists, it's best to call in a professional HVAC technician to diagnose and repair the issue.