My 250EX won't start a puddle in ac mode. Just heats up the metal until it warps and makes a hole. Material thickness doesn't matter. Frequency, argon, balance and amps don't matter. Machine grounded to its own additional ground. Not grounding issue. Noisey Arc in ac mode. DC mode quiet arc and runs nice bead. Not tungsten or tungsten distance issue. Machine only in use a little over a year and sparingly. Need to talk to a tech or someone who had the same issue. No guessing please. Need technical expert. Tired of wasting argon and have work to do. Thx