This isn’t a simple question, but there could actually be many reasons involved. A prominent culprit is that your system is low on freon. This is often due to a leak in your system which is caused by usage over the years, creating pinholes in your system that slowly…or quickly lose freon. Only an HVAC specialist is able to come and find the leaks to repair, as well as properly charge your system to the correct pressure needed. Another common cause is due to a dirty evaporator coil, which then slows the airflow into the home, ultimately leading to the system freezing up. A HVAC specialist is able to assess any damages and properly clean the coil.