Are you welding a thick material what wire{fluxcore or solid}, what speed, what amperage, DCEP,DCEN, what gas.
I'll be glad to help but facts help dial into the problem.
pjseaman

I have the same machine but never had the problem you describe. The fan always goes on when you turn the power on. It may be you are overheating it or you may have a bad machine. Best of luck with it - I've been really happy with mine.

I'm not a service man either, but my guess is the fan should be running when you turn that baby on. I have another brand of the same welder you have and the fan runs continous. Now I have welded at full power on long continous welds and have had mine stop welding for a short time(not 30 mins). I believe there is a bi-metal overload that will open up if the machine is getting too hot, this keeps you from melting down your machine. These are great little machines, if used for what they are designed to do, if they aren't keeping up, get a larger machine with more duty cycle.
I'd check out that fan on yours, I'll bet it should be running,
John Wright

Even if the machine has a temperature controlled fan it should come on as the machine gets warm. If it doesn't the machine will then shut itself down. Without the fan going it will take a lot longer to cool down. I agree with those who suggest that the fan is a likely cause of this problem.
Bill

Just to reinforce what has already been said, the fan should be running continuously, so your machine is operating properly by thermally cutting out due to over-heating. I would return it, if new. If used, open it up and use the schematic to check the fan motor connections (after unplugging!).