Several factors can cause an air conditioner to run without blowing cold air. One common cause is a dirty or clogged air filter, which can restrict air flow and cause the unit to work inefficiently. Another possible cause is a refrigerant leak, which can cause the unit to run but not produce cold air. Additionally, a malfunctioning compressor, faulty thermostat, or blocked condenser unit may also be the cause. It's recommended to have a licensed HVAC technician diagnose and repair the issue to ensure proper operation and energy efficiency.