Hi, GD, welcome to the forum. As far as using a machine pulse setting on AC, if that is the primary time when you see this arc wandering, then the most likely reason is probably quite simple. I cant be certain, but most likely, the background current is simply below the stable operating range for AC welding with all other variables remaining the same as when you are at the peak current. My suggestion is either A) use a higher background current when welding with AC ; B) Try to determine if machine pulse settings are actually contributing to beneficial results for the given task. More often than not, AC welding is less likely to be a good application for pulse settings at the machine. You could try adjusting some other parameters, but I'm not sure pulse is going to do much good for you with this application. I would try other strategies and see where that leads you.
- Alex Weeks