just replaced the core nov of 2012 and i know the blend door is actuating. feeling the hoses from the core one is significantly warmer than the other, and at a stand still i can feel some heat coming into the cab. otherwise, i have no real heat in the truck. it worked year before and then suddenly wouldn't work anymore. thermostat is new and coolant levels are true.

is there another vacuum actuator in line of the hoses that i am overlooking?

thanks!!

 

well you have missed something.. Is the coolant level in the tank up to the full mark ? If you have coolant, new heater core, thermostat is working, and blend door is OK, then you will have heat .
With NO vacuum at all, the electric blend door should be able to set at "HOT" and all the heat will come out the defrost. The selector **** moves several vacuum operated doors to direct the heat, not control the temp.
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What is the temp gauge doing ? Normal position ?
How do you know the thermostat is working ?
How do you know the blend door is actually moving (not the actuator)?
Check for proper coolant level.

I will attach a drawing of the air flow system below. Only the blend door controls the temp.

 

https://www.ford-trucks.com/forums/9...-please-2.html

 

That means that you do not have adequate coolant flowing through the heater core.

Provided the engine is actually at operating temperature and the thermostat is actually working correctly, the usual causes are:

1. Low coolant level.
2. Air bubble in the heater coolant loop.
3. Restriction or clog in the heater coolant loop.
4. Worn out water pump impeller.

Not from the factory on a half-ton pickup. You'd have to do a visual exam to see in a PO had installed one.