There are many things that could cause this – some easy fixes you can try on your own, others you’ll need a technician for.
1. It’s always a good idea to check the fan setting on your thermostat – it could be the fan is set to run constantly (instead of only when the cooling system is engaged).
2. Making sure your HVAC filter and outside AC unit are clean is another good way to troubleshoot.
3. Finally, it could be the circuit breaker in your outside unit. If it’s tripped it’ll keep blowing air without cooling. If the outside circuit breaker trips repeatedly you should get it checked out by a professional.
If none of those work, it could be a refrigerant leak, duct leak or a bad compressor – all of which require an HVAC technician to resolve.