Try changing the polarity anyway. The tungsten balls on DC when the
polarity is wrong. I don't know anything about your particular machine
but if it is possible to swap the leads then do that. You can also
check the voltage polarity with a voltmeter. The tungsten should be
negative with respect to the ground clamp. A DVM may not give you a
good reading if the welder is an inverter welder though, so you may
need to use an analog type.
Another possibility is that the welder is fried and it is putting out
max current all the time. When solid state devices fail, they often fail
with a short circuit across them, which would put max current out all
Harbor Freight welders do not have a good reputation. There are reasons
that they can sell them as cheaply as they do.
I had the same problem when I started welding with my Lincoln 175. make sure
your shielding gas is on, you have a good ground. Your tungsten is clean and
sharp with no contaminants, your amperage is set correctly, your work is clean,
and you hold the tip close to your work...without touching it (that is unless it
is a scratch start machine). Last thing to check is that your torch is
As I said, when I first started welding with my welder, this would happen to me
every time! That's how I developed that check list above! All operator error!