Best way to determine the source of a home leak

[Stephen Lynch]

Hi there,

Any thoughts on the best / most cost effective way to determine the source of a leak? The tenant went out of town and when they returned the paint pulled away from the drywall. Upon inspection, the drywall was completely dry and hard/not sinking. I cut a hole to identify the source and it looks like it was coming from the HVAC (currently set to heat). 

The HVAC company inspected it and said no leaks were detected from the condensing line. I can clearly see moisture on the wood under it, but no signs of a leak upon my inspection as well. I intend on spraying some anti-mold and letting it dry out.

Any advice on the best next steps? For now, I told the tenant to monitor it and didn't patch or paint below.


Thanks,
Stephen