Air Conditioners cool the space and eliminate excess humidity by passing warm air through the cold condensation coils that are located inside the air handler.
Condensation forms on the coils and collects in a catch basin (drain pan). When the condensation mixes with microscopic biological particles such as dust, pollen, pet dander, and airborne germs (when you cough or sneeze), a thick jelly-like mucous called "Zooglea” starts to form.
Zooglea becomes sticky and gummy as it builds up inside the condensate drain pan & condensate drain line, eventually clogging the PVC pipe causing the AC to either shut down or the drain pan to overflow.