A friend brought me one to look at as the case cooling fan would not stop running. Yours does not have this. For pics see: https://golbornevintageradio.co.uk/forum/showthread.php?tid=9434

This is what I did for him in a write up and giving it back.

The pump is two stages. Motor top right (your first pic) drives a simple fan that gives airflow to the piston pump left. This is driven by the motor, middle left, I didnt get this to run or draw current all out on the bench. Kasper’ blog indicates there is a low psi setting and it runs in the higher setting above 0.8 psi. Even back in the case and set above 0.8 psi I wasnt sure it was working. I didnt have the operating instructions.
The driver device for the cooling fan has gone short circuit so it was on all the time. Being surface mount this cant be repaired without specialist equipment and circuit and layout details. What I have done is wire this in shunt with the top right motor.. When this runs so does the fan which only takes 120 mA. Note it wouldnt run if the high pressure pump runs alone but I believe this doesnt happen. Also, it wont run during battery charging so take care. We have all seen these batteries catching fire on TV.

On the Blog he has the following:
“… but the case does get almost too hot to touch (especially closer to the air connectors).”
“… need to replace the circuit board which started to melt the USB terminals it totally overheated could’ve even caught fire.”

This is maybe the reason of fitting the case fan. It is very tiny and I could blow as hard … but not for so long.
Note: No case fan is shown in Kaspars version and the circuit board is different.
The currents involved are large and would not have been possible before modern Lithium batteries. I measured the top right motor drawing 7 A plus when it settled down. Kasper says the piston motor takes less at 4 A..

Somewhere I picked up that the unit should not be run for more than 30 mins. Its surprising with those current drains that it can manage this long.