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On my Freightliner chassis , there are shut off valves beside the transmission on both heater hoses .
Freightliner routes the heater hoses to the front of the chassis , with the valves shut off so the cooling system can be filled at the rear of the coach . Coach builder hooks up the dash HVAC system , opens the valves and tops up the coolant .
Some owners turn the valves off for better A/C performance.