To unclog an AC drain line, several effective methods can be used:

1. Turn off the air conditioner first to prevent water overflow.
2. Locate the drain line access point and remove any cap or plug.
3. Use a wet/dry vacuum at the end of the drain line outside to suck out debris.
4. Pour one cup of white vinegar or bleach down the drain line to break down algae and mold and disinfect the line.
5. If accessible, you can flush clean water or use a garden hose to push out debris.
6. Air can be blown through the line using an air compressor or bicycle pump, taking care not to splash water.
7. Use a drain snake or electric snake to manually remove tough clogs.
8. Regularly use vinegar or bleach monthly as preventive maintenance.

Each method may be effective based on the type and severity of the clog. Beginning with a vacuum and vinegar or bleach treatment is a simple and natural approach, while snakes and air pressure work for tougher blockages. Always ensure the AC is off before unclogging to avoid water damage or electrical issues.