Turn off the air conditioner at the thermostat and breaker
Locate the condensate drain line near the indoor unit
Find the drain line access point or cleanout cap
Remove the cap from the cleanout opening
Check the drain pan for standing water or debris
Use a wet/dry vacuum on the outdoor end of the drain line
Seal the vacuum connection tightly with a cloth or tape
Run the vacuum for several minutes to remove sludge and blockage
Flush the line with warm water
Pour a mixture of vinegar and water into the cleanout opening
Let the solution sit for 15 to 30 minutes
Flush the line again with clean water
Reinstall the cleanout cap
Turn the system back on and check for proper drainage
Repeat cleaning regularly to prevent clogs