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cabin heating problem


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I got Mack 2006 cxn 613 Vision which heats the cabin very weakly. I've looked and the hoses are fine (nothing is blocking them), the valve is open, and the heating core is not clogged. What can be the problem for the inadequate heating? Is it there a problem with the thermostat and if yes, then where is it located?

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What does the temp gauge read? Does the truck go to the normal operating temperature range? Do you have defrost and other functions on the dash controls? If it is operating in the normal range and you have full functions of AC, defrost and vent, I would look at the blend door to see if it is fully going to heat. That setting with the dash controls as that is what varies you temp. Paul

"OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK"  Thomas Edison

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dont forget some trucks do have valves on both hoses, I used to put another one on every truck I ever worked on that only had one if I got into the cooling system, one on the head and one on the block. Make sure the inline heat control valve is opening all the way try to move it by hand make sure its not sticking, and as above check the blend door under the dash to make sure it closes completely, also if the heater hoses are not hot 10-12" from the firewall the heat valves are closed the radiant heat from the engine will be enough to get the water in the heater hoses to operating temp even if the heat control valve is off and it is not completely circulating, check the water valves themselves to make sure the valve is opening when you turn the handle sometimes they break or the splines strip and you just turn the handle not the valve itself.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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..still fighting with the same problem...I took whole cabin console apart,and did not find any extra valve.Blending door looks working good.All control arms are OK.I have removed heating core and checked if any clogged,but none.Also valve next to engine block is not stuck.But after reassemble I have noticed even less heat is coming.

I wonder why hoses are not hot or worm at list.Something is blocking circulation.I will try to replace thermostats.Are you think it's make sens ?

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If the engine is hot the hoses should get hot no matter which position the control valve is in.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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Just for the sake of trying it out, block half (or more) of the radiator with a piece of cardboard and drive the truck for a while, if you get more heat with it blocked then your thermostats may be stuck open and continuously circulating not allowing the temp to get high enough for good heating. Watch the pyrometer while you are driving as you will also be blocking the airflow that cools the intake air and your exhaust temp will get higher than normal, in cold temps with a stock fuel system it should never get too hot but make sure to watch on hills that it does not exceed 900-1000 degrees.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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..on a control panel I got 3 knobs:fan speed,cold/hot and 3rd- position knob.Way of controlling temp is by opening and closing mixing door if I'm not mistaken.I have noticed that somehow coolant did not come out after I've took out supply hose from heating core (in reservoir level is OK),maybe valve by the engine is stuck? i have to wait until Saturday and freeze for two more days...

Thanks guys for all helping suggestions.

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...I'm still stuck with the same problem as before. I replaced two thermostats and a valve, I took out the heating core again and still nothing.When I let the coolant flow through the heating core, it instantly become hot, but when I attach the outflow, then nothing works. Any other ideas since there is no valve on the outflow. I don't see any signs of leaking/pushing coolant out of the system.

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Is this a sleeper truck? If so the lines may be run in series and the sleeper control valve could cause this issue.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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Bulldog is right..for some reason when outflow is attached to the engine,coolant flow is somehow blocking.It's a day cab.Now I'm scared to death,because what I'm thinking now is eater compressor,EGR or leakage from piston ring,which make pressure and stopping,blocking coolant flow.Tomorrow I will have to go to Ripon ,WI...wish me good luck with temp 18 F and snowing.... :(

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Take a picture of the fittings the hoses connect to on the engine and post it here please, if you are getting water to the core but it won't flow back to the engine there is something closed or blocking I doubt its making pressure and stopping it, you would have a pressurized coolant tank and lots of stuff coming from the crankcase vent tube.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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just a thought... Is your coolant level low? if it is water might not be able to get to the heater core being that it is one of the highest points the coolant flows to... if its topped off it has to be a bad valve or blockage. does that water pump have a nipple on it that is capped off or is there another nipple you can plumb into?. you might be able to run a hose right off the pump and see if that corrects the heat?

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Only one coolant hose from heater core attaches to coolant manifold second line from heater core attaches to lower steal surge line that goes up to coolant overflow tank the other coolant fitting on cooant manifold goes to raycore fuel heater out of heater and back to lower steel surge line .. Looks like both your heater core lines are attached to water manifold from angle I see and if it is this why no heat same water psi on both lines no flow.

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Yeah one of those hoses need to go to tank not back to the same manifold.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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