Turn off the AC.
Find the AC drain line.
Use a thin brush and push it through one end of the pipe to the other.
If it’s not cleared, use your wet/dry vacuum, and attach it to the end of the drain line and vacuum for a minute.
Locate the vent tee of your AC and remove the PVC cap.
Pour a mixture of bleach and water through the drain line. If it can make it all the way, your drain line is cleared.