Joe,
Your C 12 only uses the serpentine belt to run the alternator and A/C compressor. Everything else on the engine like the hydraulic fan pump, air compressor, and water pump are direct drive from the engine. Your problem sounds like a low coolant level. If the coolant is low or the thermostat is stuck closed, the wax valve will receive no hot coolant, so it will not activate the fan. You need hot coolant circulating in the cooling system for the fan to engage.
Gerald