Arrived on site and customer stated that they had a leak coming in the ceiling around the air duct vent in the downstairs bathroom. It was stated that the original technician was from the HVAC department, and upon his examination, stated that it was a plumbing issues . I offered the customer the option to cut open the drywall as it would be the only way for me to determine where the lake was coming from. Once I cut up the ceiling, I was able to fit my head and the opening and saw a drain line and a waterline, but did not see any leaks from either. I went upstairs and flushed the toilet for 30 minutes continuously. I ran the water down the drain as well for 15 minutes and continue to keep an eye on all plumbing related scenarios. I determined that it was in fact a HVAC issue because there was only an ring around the exterior of the drywall which was directly around the air duct ventilation I found no signs of water, stains or occurring water, leaks any moisture from the fixtures on the