The most common problem causing no air flow is a highly restricted (dirty) air filter. Most central air conditioning systems have a 1 inch thick disposable filter somewhere on the intake side of the air handler/furnace. It could be in a “filter grill” located in the house or in a “filter base” if located in a mechanical closet where the air handler/ furnace is, or in a “filter plenum” if air/handler/furnace is in the attic. This size filter should be replaced at least every 90 days or more often. Some systems have thicker filters that can go for 6 months to a year before requiring replacement, these are usually found in the mechanical closet or in the attic. Highly restricted filters reduce air flow considerably and possibly completely.
Regardless of the thickness if the filter gets overly restricted from debris it will cause low air flow thru the cooling coil, this in turn allows ice to start forming on the evaporator coil. Once ice starts to form it often escalates to blocking the air flow and causing other problems. In the winter it can cause your furnace to overheat and shut off on safety switches in the equipment.
Things you can do: Change / Check that Filter every 3 months
Another culprit causing low or no air flow is the air handler/furnace blower motor, should the motor stop turning or if the squirrel cage becomes blocked air delivery stops or diminishes and once again the evaporator coil will freeze adding to the problem. Paper, animal hair, dust and dirt can collect in the blower compartment and cause this, or the motor can fail outright.