I think that was in Season 8.
Iv'e often wondered about that particular scene in Andy's Vacation when he tied Alan Melvin to the tree by the lake with his arms wrapped around the tree. Andy said he had to go to the other side of the lake for help so he was going to leave him there tied to the tree and he said:"I'll freeze to death" so Andy takes off his coat and just sticks it over him and sorta tucks it in over his shoulders, then Andy takes Alan Melvin's jacket and puts it on, so they ended up switching jackets. I guess that's why Barney and Gomer didn't recognize Andy when they came upon him from behind down by the lake as he was messing with the rope on that rowboat. A sitcom can be a curious curious thing. "Anxiety magnifies fearsome objects."
I have often wondered how Andy so easily apprehended big “Fred Plummer” given he was the “Sheriff without a gun”. Maybe Andy was also taking some of those Judo lessons!