Heat when the heat ain't on

[mikeconner1]

I've got a thing going on with my '68 longbed that isn't a problem right now cuz its cold out, but about June its a touch aggravating. For some reason, I've got hot air ALL THE TIME out of the floor heater vent box ( I 'spect its coming out the top as well) even with the heater valve completely closed. Back a couple of years ago, I replaced the leaky heater core, and while I had the assembly off, I adjusted the function control that moves the mode door so that it would shut more securely, thinking at the time that this was the problem. That however didn't fix squat. I still have hot air coming in, even with everything shut off. So, why do I have hot air there, or for that matter, why is there ANY air flowing through there, hot or cold? With the heater valve closed, there shouldn't be any hot water in the core, so that's puzzling, but even if that was shut off completely (which it apparently isn't, even though I've even manually closed that valve out under the hood) so where's the heat coming from, and where's the air coming from after I stop the heat, should I be able with your help to figure out the heat problem?

[Dragon]

You have a valve under the hood that is controlled by the temp slider. The valve plate inside rots away. My 71 did that. There is also fools who remove the valve for some reason.

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[fordman]

did you sitch the lines to the heater core by mistake. they have to go on the correct way to stop the water from coming into the heater core. and i forgot whihc side its suppose to be on. i think it is suppose to be on the water pump side.or the valve could be bad, or the heat is just coming in from the vent and engine heat. mine is like that. it gets hot inthe cab while driving it.

[Dragon]

Top of the water pump passenger side to return, Valve goes to top of intake above thermostat though it would only matter after the hose water absorbed the heat all the way up to the core.

[sideoilerfe]

Do you have an FE with the heated carb spacer? If so, it might be plumed wrong. I made that mistake once and had the same problem. The spacer hose should return on the opposite hose than the heater control valve and as stated above, the valve should be on the same hose that is connected to the top of the intake. If the carb spacer hose is connected to the valve hose after the valve then you'll still get coolant into the heater core and the valve becomes useless.

[mikeconner1]

Dragon, let me be the first to say "HUH?" I think you're saying the water pump hose connection goes to the far right connection on the core and the other line will hold the control valve, and comes from the intake to the left core connection. But I really don't know what the last part of your message is saying, gimme that one again, slower, like you're talking to a very slow, dimwitted wrench turner (as I am <GRIN>).

[Dragon]

Yep I was in a hurry.

You got it right as where the hoses go. If you reversed them the core would get warm by heat conduction up the water in the supply hose to the core.

[mikeconner1]

OK, I drove the old girl to the shop today, and checked my routing on the heater hoses. I had replaced the hoses when I out the new carb & intake on, and thought I might have things reversed, but no dice. The water pump connection is running to the far right core connection, and the intake hose to the left side, and that hose has the heater control valve in it. The valve is new, because I had this problem with the old 2BBl set up, so I changed it when I updated to the new 4BBL since I had all that stuff off. So there's two things I don't understand, 1) Why is there heat coming through even when the valve is shut off, and 2) Even if it wasn't heat, why is there air moving through the vents when everything is shut off, whether the air is hot or cold? Shouldn't be anything coming out of that floor vent box with both levers off, so I don't know what is going on. Suggestions?

[fordman]

ok the heat box connects to the firewall and has a fresh air vent through the passenger kick panel. which cant be closed off. there is inside the heat box a system of doors. that are or were covered with foam. to stop the fresh air into the cab through the heat box. radiant heat can travel through water and into the water in the heater core. it may take some time for this to happen. if the foam on the vent doors is worn out it can let air flow through the heat box and get warmed up by radiant heat from the engine water. thus produce heat into the cab via the heat box. if this is doing this when not driving then the fan motor is not shutting off completely. that could mean a bad switch or a bad resistor. either or. it would have to be tested to find out which one. unless someone has wired around the switch and or resisitor to make the fan blow all the time only on low. thats the best explanation i can give on how the system works. the hot water will only circulate through the core when the heater hose valve is open. radiant heat can after a while radiate into the rest of the system but it can't circulate if the valve is closed. valve open faster heat. valve closed super slow heating via radiant heat. let us know if that does clear it up for you.

[Dragon]

There are two different valves one that is open when the cable is pulled closer to the cab and the other is open when the cable is pushed farther from the cab.

My 71 and 69 are the ones that open when pulled close to the cab, closed when pushed away.

[fordman]

oh i missed that. the valve could be on backwards. duh.

[fomocodave]

are you referring to when your going 50 mph and you feel heat coming out of the vents even though the fan switch is off? its that silly fresh air boot on the passenger side, it really has no closed position. it either directs air into the cab or into the vents. i blocked mine off.

[FLATBEDFORD]

There are two different valves one that is open when the cable is pulled closer to the cab and the other is open when the cable is pushed farther from the cab.

My 71 and 69 are the ones that open when pulled close to the cab, closed when pushed away.

Have you tried setting the temp control all the way to hot?

[fordman]

that would be a good way to check it.