Lincoln Bullet Welder 250 take 2

Hi there! My Lincoln Bullet welder has finally arrived from Queensland. The guy had it in his ute and was telling me it weighted 300 kilos but a bit of a push around told me it was not even 300 pounds, so offloaded it on my trailer and off I went to a repairer who knows the machine. After a couple of weeks, the machine is ready, he is very happy with how it works, very smooth. Plenty of brushes life left in it, amps regulation works very well, the controls for amps and volts are not worn, however ... you where waiting for this right? ... he tells me that he measures the voltage with the machine running with no load and he gets 44 V, yet changing the voltage by turning the knob up or down does not change the reading. He has no way to measure the voltage whilst welding and does not know if the control may work when welding or not ... (?) anyone understand how this voltage control is supposed to work? Your answers as usual are very appreciated