Autotransformer fan not engaging

Part number: ITR050362041 – Isolation Transformer 3600W Auto 115/230V

I had an issue with an Autotransformer in a marine system where the fan wouldn’t come on and it would quickly overheat. I tested the fan and the motor worked so I had to conclude it was an issue with the thermostat

I returned it and got another one and the fan still has not come on even though I have a 20A load connected in ambient temp of around 83 degrees F.

Seems the fan should be coming on under those conditions but it hasn’t overheated yet. Does anyone know the specs for what temp/conditions the fan should engage? Did I get two broken units in a row?

Thanks in advance