Like I posted earlier...Norcold OEM t-stat senses Condenser Fin temps (condenser is top finned component in outside compartment) and starts fans at 130*F condenser fin temp and stops them at 115*F condenser fin temp
Nighttime ambient air temps are typically cool enough that condenser fin temp would NOT get hot enough to need fans
Daytime temps...FANS are used to increase volume of air flow across backside of cooling unit. Higher volume of air movement....better heat removal.