Hi guys - new to the forum, and new to the 7.3 diesel. Have a 1996 2WD dually with very low miles (69000) runs like a champ. Problem is no cabin heat, both sides of heater core get hot, new thermostat - removed cover plate over heater core to check for flap operation, pens stuck etc and all is working. Blower works, all controls too - very mystified, hope you can shed some light (well heat !!)

 

First of all WELCOME to the site. This is a bump for you, soon somebody chime in here.
Do you need heat?, oh yea you are VAPOR. LOL. JK.
Good luck.

 

The center temp selector is cable operated and it sounds like it is not opening the heater door to let the heat into the cab. With the heater door closed it does not let the blower air move thru the heater core (it directs it across the A/C core). So the cable could be broken or the came off of the back of the control arm or off of the door arm (both of these are plastic tabs that the end of the cable goes over (the ends have looped coils on them). Hope this helps.

 

i went through this with the 96 superduty plow truck back in december.
you need to open the heater up again.
on the left of the heater core is the blend door that the hot/cold **** cable controls. when turning the **** it should be very easy to move, and you will see the cable push a small lever on top of the blend door
what i bet happened is that something fell down into the ducts and jammed the blend door, since you said you removed pens and the like.
i had to remove the heater core to get in there and force the door open to let the air go through the heater core.

 

Thanks for the reponse guys, I checked the blend control and the flap opens and closes as it should (nothing trapped in the door). I'm wondering if the core could be only partially plugged - it gets hot both sides of the core and hot to the touch on the surface. I can't find anything physically wrong unfortunately - luckily I don't drive the truck in the winter, maybe it's just the way it is.

 

Have you had any recent work done to it?
Can you hook a garden hose up to it and watch the flow for obstructions?
Could the coil be so dirty that there is no heat transfer?

 

if coolant is flowing through the core and the blend door is working properly, the only other thing i can see would be no air flow through the core itself like Ian said.

pop the core cover off and using compressed air see if you can blow through the core and feel air flow on the other side.