I work at a small box factory and we are having a problem with a foul smell. It is at its worst when we return on Monday morning after having the HVAC shut completely off all weekend. As the week goes on the smell seems to weaken each day. We cannot find a specific spot where the smell seems to come from it just seems to be all around the office area. At first we thought it might be a plumbing gas problem but we have checked all our p traps and everything there seems in order so we are looking now into the HVAC systems. Has anyone ever experienced any problems like this. Maybe a bad funk in the condensation collection tray? Any advice would be appreciated.