77, F250 with a 460.
Heater just blows cold air.
I changed thermostat , didnt make any difference.
Checked controls the seem to move right.
Was thinking about blowing threw heater core? Anyone know which hose is in and which is out?
One comes right off waterpump , other comes off engine?

 

A/C equipped or not?

 

The return hose goes to the block and it should be pretty much as warm as the one from the pump while it's running. If it's not then the core is plugged or somehow flow is being obstructed. Blowing through a clogged heater core won't fix it because of how it's made inside.

 

so if blowing threw it wont work , do you have any other suggestions?

 

I would disconnect the hoses and check the first to make sure your not going to push any built up crud in them into the core. Then reconnect them to the core and flush with water to check the flow. That will give you an idea if it is clogged up or not. Put the end opposite your water hose into a container to catch and see what comes out. Depending on state of the rest of the cooling system, you might want to consider a chemical flush and see if that helps.

None of this should make anything worse.

 

If you want to know if water is flowing through it just warm it up and feel both hoses. if both are hot it's flowing .

Unless you have a real mess it shouldn't be plugged off. if it is plugged it has to be replaced.

 

Have you checked the vacuum controled heater valve in the hose to firewall for operation? It opens with vacuum which is controled by heater controls. A rotted vaccum hose maybe or bad valve? Original Ford one looks a little different, it is metal too.

I forget if my truck had one with just heater before I added AC though. Maybe it came with the AC parts?

 

No valve if heater only, OP never answered if AC truck or not. If op has a factory shop manual should be a flow chart or guidance to eliminate faults.

 

I figured as much, just wasn't so sure ... been so long ago.

 

No AC............................

 

I was able to get another year or 2 just by swapping hoses at the core. Was 2 afraid of making it leak trying garden hose pressure. It's a no cost try. Mine didn't start working again till I kicked it down to pass.