Failure to clean and maintain drain lines and pans can lead to severe consequences, including water damage, mold growth, and system failure. Clogged drain lines can cause water to back up into the HVAC unit, damaging internal components and leading to costly repairs. Additionally, stagnant water in the pan can foster algae and mold growth, which can spread to other parts of the system and even contaminate indoor air. In extreme cases, neglecting drain line and pan maintenance can result in system failure, requiring expensive replacements or repairs.