When an air conditioner's filter is clogged, the unit cannot operate efficiently. This inefficiency can manifest itself in an increase in the humidity of the air emanating from the air registers in your home. A clogged filter prevents an air conditioner from taking in enough air to keep the air cycling within the unit. This leads to a decreased amount of water being removed from the air, and an excess of humidity in the air returned to the home.
Condensation Pan Issues
When indoor air is pulled across the cold copper coils inside your air handler to be cooled, these coils "sweat" from the temperature differential. This sweat is comprised of the humidity in your home and condensates on the coils before dripping into the condensation pan. The pan has a small drain in its center, which drains water away from the system and dumps it outside the home. If this drain is clogged, water cannot drain and the air conditioner is less effectively dehumidifying the air it processes.
Condensation Drain Trap Issues
Condensation drains have traps, just like any other plumbing drains in the home. A trap is a small elbow of pipe that stays filled with water and prevents air from traveling back up the drain and coming into the home. If the trap is malfunctioning, the air handler can create a sufficient vacuum in its system to suck air in from outside the home by way of the condensation drain. This air, as humid as the air outside, is then cycled back into your home and creates excessively humid conditions.
Low Coolant Levels
Over time, air conditioners in the home can require recharging just as air conditioners in your automobile do. If the coolant levels in your air conditioner are too low, the system will be less efficient at both cooling and dehumidifying the air inside your home. The result will be an air conditioner that spends much more time running and rarely cycling off as well as excessively humid indoor conditions. Consult a local authorized service center for your particular brand of air conditioner as coolant is not user serviceable.