For the Magnum inverter in my Berk, there are 2 fans. One is internal to the inverter and controlled by it directly. The other is the exhaust fan on the compartment. That fan is controlled by a heat sensor that is attached externally to the inverter on the end mounting plate. It is added by FR to help keep the compartment cool based on the inverter temp. Are both fans functioning? I would submit that if the compartment fan is running in 35 degree temperatures, the unit is overheating due to an internal fan problem and the unit is much hotter than the surrounding compartment temp. I don't see my compartment fan run unless the temp is above 80.
I'd suggest you call Magnum. They've been good to work with when my unit failed last year.
2015 SOB 5th Wheel
2013 Chevrolet 3500 CC, DD SRW
1 Wife, 2 Kids under 5
Camping nights: 2015 - 19, 2014 - 39, 2013 - 48