Heater not working?

Try replacing the thermostat and make sure the heater core is not partially clogged-up don't work come on back.

Is the coolant full? WIth the engine hot, running, and the heater on, do both heater core hoses get hot?

Test the thermostat might stuck open and also the heater core if its clogged-up/coolant level

Is your heater control valve oppening properly? To test feel the heater core hoses, if they are hot like usually then it is probably the blend door, if you notice they are warm not hot then you may want to check your heater control valve.

Welcome to the forum, does the blower motor work? Are the heater hoses hot? Can you check for circulation through the heater core?

The heater hoses should go to firewall, passenger side, they attach to the heater core. I Tried to find a picture of attached heater hoses, couldn't find one? Two hoses from engine block to heater core. If I take a hose loose, I take loose from engine block, bump starter, no start. See if coolant comes out of return line. I haven't found anything on heater hose routing.

You have an old case of "somebody put the wrong coolant in" and it reacted and became sludge. Usually hot water out of a garden hose can flush it out, but if its real bad, be prepared to replace the radiator. As far as no heat goes, that can be flushed out 80% of the time. Disconnect the 2 heater hoses that go the the heater core, and put hotwater through a garden hose through one hose, you should see nasty brown sludge come out of the other. If so, then you have flow through the heater core, and saved 8hrs of time to replace it.

Try flushing the heater core

Remove two heater hoses
( engine side)
Use a water hose run throw one and watch the pressure and amount of water coming out throw the other side
untill clean and good flow
place back and run truck

Good luck

If you always get heat, you need to check the blend air door. It determins if you get heat or AC. If it is stuck, then you may not be able to shut it off.