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