Your thermostat typically has fan positions available in "Fan On", "Fan Auto" or "Fan circulate". Typically we use our air conditioners to cool and dehumidify our homes. When you are "cooling" you are also removing humidity or water from your home as well.
The air conditioner has a coil in it. It looks very similar to a car radiator. While in the cooling mode very cold refrigerant is circulating through that coil. As the air moves through that coil, the heat in the air is absorbed into the refrigerant. The water in the air hits that cold coil and condenser onto it, just like a glass of iced tea. It moves down the coil, puddles into the drain pan and goes out the drain line. That's how the humidity gets removed from your house. When your air conditioner cycles off that fan needs to cycle off too. DO NOT run the fan in "Fan On" or "Fan Circulate" while you are in the cooling mode.
When you run the fan after the compressor cycles off all the water that's on that coil gets evaporated back into the space, it elevates the humidity levels, and overtime can become an Indoor Air Quality problem. Humidity levels over 65% R.H. are dangerously high for creating a favorable environment for desirable microbial growth. DO NOT RUN "FAN ON" or "FAN CIRCULATE" while in the cooling mode.