We are a Dodge family. We have a 1975 Dodge D100, a 1995 Dodge Grand Caravan and a 1996 Dodge Ram 1500. With all three vehicles the heat continues to come out of the vents, even when they are totally off. Only the van will cool off if switched to the a/c and the temp moved to low. No one seems to understand why this is happening.The fan is off and the temp is set on the cold side, except in the older truck, as it seems to bounce back after being moved over. I know its confusing, but to have hot air blowing in the summer is crazy hot. And to not have just one doing it, but all three is even crazier.
Well the reason why is because the heater core is hot and flows heat slowly through the vents. The only way to fix that is look at the firewall and you will see two hoses if you disconnect it you will lose a bit of antifreeze. What you do is get a piece of pipe that fit inside the hose with the clamps and make sure that pipe can handle the heat. That way you don't have to worry about the heat flowing through or if you make your own homemade valves and connect the pipe so all you got to do is turn both valves to use the heater core or the pipe to have the antifreeze go around back to the motor. My truck is set up that way it is quick and easy. No problems at all.
There is a shutoff valve that must be defective. Pretty sure you can easily see it on the 75 but don't know about the others. On the 75 I think it's under the hood on the right top.
When you say totally off, do you mean the fan is off? If the temperature setting is still set to "HOT", coolant from the engine is still circulating through the heater core but the fan is no longer blowing across it to blow hot air into the passenger compartment. However, the heat from the heater core is still there and finds it's way into the passenger compartment. This is what I do. On a cool day like 75 Deg F, I set the temperature control as cold as possible and set the defrost to the lowest setting. It blows out cold air just as if the a/c was set to "Cool".Edit:If you don't mind making it look ghetto, you could add (if it doesn't already have one) a manual 3-way valve. One setting to go as normal and the other to bypass the heater core so that no hot coolant reaches the heater core. Unless the cab fan is getting outside air from the engine compartment and not from say the top of the engine compartment like the inlet ducts by the windshield.
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