Hotpoint fridge freezer FF68

The fridge temperature is being controlled ok , presumably from the fridge thermostat, but the freezer isn’t cooling at all, [nor is the fan running but no doubt it won’t if the freezer is warm] . I suspect it’s short of gas – haven’t tested it yet – but can anybody tell me what the freezer cabinet thermostat does? There doesn’t appear to be a solenoid valve to control one section, so why are there two thermostats?

Thanks

Geoff