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CVD's avatar
CVD
Explorer
Jan 02, 2017

Heater Core Replaced, Now Blows Cold Air

I had a leaking heater core replaced on my 99 Winnebago with a Freightliner XC chassis. No more leaks, but now the dash heater only blows cold air. I suspect my local truck repair guy (who knows heavy trucks, but necessarily RV systems), didn’t reconnect something properly.

Here’s a pic of what I’m looking at. I imagine that “valve” on the heater hose (with the pale green wire) is what controls coolant flow through the core. Anyway to test it? Anything else I should check?

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  • amxpress's avatar
    amxpress
    Explorer
    Jan 03, 2017
    Like Krusty said, very likely an air pocket is not allowing circulation through the heater core. Touch both hoses where they enter the box, after the engine reaches operating temperature, if only one is hot , apply vacuum to the nipple where the green wire is connected. Oh, that's a hose not a wire. If the hoses still aren't hot to the touch, bring it to a shop that can bleed the air from your cooling system. Also make sure your water pump is circulating the coolant.
    Good luck
  • Krusty's avatar
    Krusty
    Nomad II
    Jan 03, 2017
    There is likely air in the system due to the long lines and the placement of the heater core. First check the coolant level and make sure it is full.
  • Tim_Nowicki's avatar
    Tim_Nowicki
    Explorer
    Jan 03, 2017
    One would think that the mechanic would test the system before it goes back to the customer. Apparently not.

    Tim
  • slickest1's avatar
    slickest1
    Explorer
    Jan 02, 2017
    cbeierl wrote:
    My Freightliner chassis has yellow shutoff valves for the cab heat water lines back near the engine. You might see if you have those and make sure that they are open.





    Like said above or follow the heater hose up to the engine there may be a valve type tap that is shut off. The mechanic may of shut it off so the antifreeze would not leak out while changing the core and forgot to turn it back on.
  • cbeierl's avatar
    cbeierl
    Explorer
    Jan 02, 2017
    My Freightliner chassis has yellow shutoff valves for the cab heat water lines back near the engine. You might see if you have those and make sure that they are open.



  • turbojimmy's avatar
    turbojimmy
    Explorer
    Jan 02, 2017
    Vaccuum should open that valve and let the coolant into the core. You can test it with a hand vacuum-pump. You should have vacuum there (can feel it if you put your finger over it) when you're calling for heat.
  • Bill_Satellite's avatar
    Bill_Satellite
    Explorer II
    Jan 02, 2017
    On the hose right behind that valve is looks like there is a cut-off valve. It would have sort of a slider arm that rotates 45-90 degrees and opens and closes the fluid access. Is that what I am seeing and if so, have you tried moving that to the opposite position?
  • All_I_could_aff's avatar
    All_I_could_aff
    Explorer
    Jan 02, 2017
    With engine running a few minutes, feel both heater hoses to see if they get hot. If not, no or little coolant flow. Possibly the vaccume controled valve you mentioned.
    If both hoses are getting hot, likely the blend door is not operating, possibly bumped off during the repair.

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