I have a 79 Super Camper Special that has many issues. First- no heat. The truck was originally equiped with air. I removed most of the ac components when I replaced the 460. I am not sure if all 79s are like this, but looking at the back of the heat/vent/ac control it is all vaccum line controled-no wire to operate the the door for heat/cold air. From what I can tell from the Haynes manual- it looks like the only difference between heat and cold air is a door which directs air over the heater coil? Is this right-for an ac truck also? if so can I manually operate this door? The other thing that is bothering me is if the vaccum line is not operating- does it have a hole in it causing a vaccum leak? The second pressing issue is the Haz flasher- I have owned seveal 73-79 fords and know the electical system is proun to corrosion this time of year and many of these trucks have had there wiring harnesses spliced many times. All the lights work except the haz flasher. Fuse is good- and I swithced out the flasher. I have seen them stay on solid- no blinking when there is a dead short. But nothing on this one- any suggestions on how to test?

 

I was just messing with a simular problem like this earlier tonight. The heater wasnt working so it turned out to be the vacuum operated valve on the heater hose. It wasnt opening to let the water flow.

 

First dumb question, do you have enough coolant?? This sounds stupid, but your heat wont work if coolant cant get pumped thru the core. Do you hear any kind of hissing noise when you move the controls around? Did you check your vacuum line inside the cab, to make sure the correct one is hooked up and not broken or kinked?

 

I just replaced the 460 and radiator- coolant is new and full. I understand how the non ac truck heat works- pretty simple- is the ac truck the same- the heater hose going into the core is hot and the fan works. In a vaccum operated system what operates the selecton or door that changes cool to hot. I pulled the ac/heater controls and looked at vaccum lines- all are attached, but I did not trace them to their destination.

 

What else is new? Prolly one of Ford's all tlme best sellers for two reasons. First it's a POS, and second, besides F Series trucks and Bronco's, many of the 1970's cars used the same one. It's still available from Ford.

D4AZ-18495-A .. Heater Valve (Motorcraft YG-146)

 

Thanks for the info- where is the valve located- under the hood before the core or under the dash? I have a chiltons and Haynes manual- both do not give have a good diagram for the heating system?

 

The heater control valve is in the heater hose under the hood. It is vacuum operated to allow the heated water to flow through the core.

 

 

Thanks for the help!

 

When vacuum is applied, the valve is closed and theres no water flow. No vacuum the valve is open and water flows. If you look at the valve theres linkage that goes from the diaphram to the valve. You should be able to tell if its moving or not. Also if you cant move it by hand or pliers then its probably stuck. You could also check if its getting vacuum by letting the truck run and disconnecting the vacuum line. If the heater controls are off a vacuum should be present. Heater on=no vacuum.