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  1. #1
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    Freightliner Century Heater Valve

    I have a '98 Century with an N-14. I'm not getting any heat to the front of the cab. I opened the valve and the sleeper has heat. Am I missing another valve somewhere?


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    Quote Originally Posted by mrbamcclain View Post
    I have a '98 Century with an N-14. I'm not getting any heat to the front of the cab. I opened the valve and the sleeper has heat. Am I missing another valve somewhere?
    Trace your heater hoses from your heater core/box for the cab from the firewall back to the engine. Is one hot and the other cold?

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    I only see one valve in the lines

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    Is your coolant level up? Basic question I know but if your level is low there won't be the volume to push the coolant UP to the heater box/core, especially at an idle. Have you tried moving the cab control back and forth a few times? Problems like this are common this time of year the first time we need heat.

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    Yes, coolant level is in the normal range. I've tried the control but nothing helps. Would there happen to be a vacuum operated blend door behind the dash like in my four wheeler?

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    Quote Originally Posted by mrbamcclain View Post
    Yes, coolant level is in the normal range. I've tried the control but nothing helps. Would there happen to be a vacuum operated blend door behind the dash like in my four wheeler?
    Vacuum/air operated possibly. Where is your other switch set? Fresh or recirculate?

    Is ONE coolant line warm and the other cold? Is coolant getting to the heater box/core?

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    I've tried it set to recirculate and fresh. Both lines feel warm to the touch. Neither too hot to hold a hand on.

  8. #8
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    The coolant does not have a flow control valve it regulates the preasure with the blend door of the heater. It is posible you heater core is plugged, especially if you do not have a water filter.
    The blend doors are air operated same as the vacuum ones, only backwards, cars have vacuum trucks have air. If you move the levers you can hear the doors change position same as the temperature control, I do not remember where the valve is but if you shut the truck off, and move the value you should hear it move, or leak. Laying on the passenger floor you should be able to see the doors move all except the defrost, it is under the dash.

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    How would I check to see if the heater core is plugged?

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    First off have you added any stop leak? If yes it is plugged.
    Second do you have a coolant filter? If no it is plugged.
    Third do you use DCA4? If yes it is more likely to be plugged
    Then run the heater at full temp heat, full fan, be sure the filter is clean, and measure the coolant temperature at the J block outlet it should be a maximum 10 degrees less than the inlet temp with the engine at 1200 RPM.