How to Troubleshoot a Hot Air System With a Clogged Condensation Line

Locate the condensation line. You can usually find this pipe outside; it's a PVC pipe that runs from the condenser inside your house.

Remove the cap from the indoor condensation line to gain access to the inside of the line. If water overflows when you remove the cap, you can almost be certain you have a clog.

Create a mixture of five parts warm water to one part bleach in a bucket or similar container and proceed to pour the mix down the line. Bleach will kill the algae, while the water will flush it out. You may have to repeat this a number of times.

Use a plumber's snake to physically prod and remove the clog if the bleach method doesn't work or you prefer this option. This may prove effective on thicker, more solid clogs that bleach and water struggle to move.

Call a plumber if these methods don't work. It may indicate a more serious issue that can't be remedied with a DIY method.