No heat 97 t100 3.4

Ok, here's troubleshooting 101.

1. What is the desired result (heat in cab)
2. What is needed to get 1. (Heat in the form of hot water and air)
3. What is missing from 2.
4. Why is it missing?

And that's as far as we need to go as this one is simple. All you need is heat/water and air. Find and fix 4 and you get 1.

Here's the basics on getting heat. The engine runs which creates heat. The thermostat stays closed to keep the heat in the engine until it reaches operating temperature, about 180 degrees. Once that point is met the thermostat opens releases heated coolant into the radiator to prevent the engine from overheating, and the smaller secondary line that lets heated coolant flow through the heater core, which looks like a small radiator. The heater core heats up to the coolant temp, the blower fan blows through the core which heats up the air it's blowing and that hot air is what heats the cab. The blend door either blocks the airflow or allows it through the core. No sensors or anything else is involved.

You said the truck isn't overheating so off the bat you know the thermostat is working. Ignoring that I asked you back in post 7 to check the heater hoses. You said they're hot. That alone pretty much eliminates the entire water side of 2. If the core was blocked no or very little coolant would flow so you would either have 2 not hot hoses if it was totally blocked, or 1 hot and 1 kind of maybe warm if it's letting very little fluid through. 2 hot hoses = waterflow = good thermostat = unblocked heater core.

1 test tells you that you don't need to troubleshoot the water side, which would include coolant level, and coolant flow, which is taken care of by checking thermostat, core blockage, flow valve and lastly waterpump.

That leaves us with air.

So to get hot air you need 2 things. 1. A working blower and 2. uninterrupted air flow through the core. Since your blower is working that means the only thing actually missing from this flowchart is airflow. Post 7.

Unless something has fallen behind the dash and is obstructing airflow the only factory installed item that would cause this problem is the blend door.

Physics says there is no possible way to have both a heated core and airflow through it and not have hot air on the other side.

 

Blend door works , it's a mechanical one and I'm able to verify it opens and closes

 

I am going to pull the heater core , although I had inlet and outlet off ran garden hose through it and it came out instantly clean

 

???????
BLEnD Door works as it should ,
I have flushed and ran water through every hose and water orifice
Took the dash apart to make sure all mechanical doors and cables are working and hooked up .the blower works at every speed , but I get cold air at feet ,vent and top of dash
The only thing that is weird is the AC light that you have to push to turn on ( green light) when I shut that light off when I switch my heat control to defrost that green light comes on then switch to any other position light goes off ????

 

Great video but all checks out