Sulphur Smell .....Epilogue

I had the same thing in my unit. Realized it became worse when we ran the A/C. Cleaning the foam filter with soap and water cured it. Seems bacteria builds up on the foam depending on humidity and other factors

The smell only occurs while we are moving. We've only run the AC twice for short periods in the last 8 days. I did a total clean of both black tanks today. Tomorrow when we hit the road again, I will check the battery compartment for smell ( the battery has a plastic cap over it with a hose to vent fumes outside the trailer) but will check anyway. BIL thinks it is exhaust from the truck coming in, though I can't see that. I just have to figure out what has changed from last year where I drove 7k miles and 1500 miles to Fla in Feb and March and after the 4th day into this trip when the oders started. The first time I noticed it was at a rest area next to a truck pouring out reefer fumes on the 4th day, so I discounted that. Then it started up consistant after that and was not around other trucks. Keep throwing things out there, maybe something will pop. I appreciate all the suggestions so far. I've got an email into Keystone to see if they can tell me where the vaccum valve/valves are, but I'm not holding my breath on that reply.