Central AC Stinks at Night
Recently, our AC has started blowing sewer smelling air after we get home at night. During the day, it doesn't run much since we cut it up to 78 degrees while we're at work. It usually smells fine the first time it comes on in the evening, but it really stinks and smells like sewage the second time it comes on. We had an AC repairman come look. The AC drain is not plugged. There is not a dead animal in the unit. The ductwork does not appear to be overly dusty. We cleaned out the toilet vents and replaced a wax ring on the master bathroom toilet. The smell is worse in the master bathroom it seems. We were thinking maybe gas from our septic tank was backing up into the house, but there is no odor coming from the sinks, tubs, etc. It's definitely coming from the AC vents. Also, you can smell it coming from the unit when it's bad. We did recently have a sewer treatment plant installed which catches the runoff from our septic tank. The plumber says there is no way the sewer treatment plant could be making it smell, but it's quite a coincidence the smell happened shortly after the treatment plant was installed. I also notice it during the day on the weekends if we've been using a lot of water, like washing clothes or dishes. We don't know who else to call. Another AC person? Another plumber? We are at our wits end and tired of living in a stinky house. Any advice would be greatly appreciated!