Performed semiannual maintenance on two heat pump cooling systems. Inspected all Performance, Mechanical and Safety Systems. When entering the attic, I found that the upstairs HVAC system had a drainage overflow into the secondary drain pan due to a clogged-up drain line that attaches into the upstairs bathroom sink. Cleared the drainage restriction in the drain line and treated with our drainage treatment. Also did the same for the downstairs HVAC system. Spoke with homeowner about having water safety switches installed on both units to avoid water damage from a drain clog; he agreed. Installed switches and programmed the wall controller for the switches to shutdown unit in the event of a drain blockage. Verified everything was operating within manufacture’s specifications for operation.