The suction line is the larger of the two copper pipes in an HVAC line set, and it carries low-pressure refrigerant gas from the indoor unit back to the compressor. This line is typically very cold and must be fully insulated to prevent condensation (sweating) and energy gain. If the insulation on the suction line is damaged, it can lead to water damage in your walls and reduced cooling capacity. You can find replacement insulation and copper parts in our store. Proper maintenance of the suction line is essential for the health of your heat pump condensers. It is a core component that connects your wall mount to the outdoor unit.