I went to HF to see if they had the reconditioned Hobart Handler 135's, which they didn't. I looked at the new one on display, and looked under the cover. I was a little surprised to see this drawing (not diagram) of the wiring that said to have it DCEN for flux core wires, and DCEP for gas shielded.
My thought is, what the heck difference does the wire type make for polarity?? I'd probably have just run DCEN for steel with either type of wire.