Then why have speeds for the blower motor? Turn the motor on, and use the flap to control how much air flows. Or why have the flap? Just use the motor speed to control how much air flows. This is what I don't get - they seem redundant, or counterproductive (if the flap is closed & the blower is on HI), which is not common in Ford designs. I can't figure out why the flap is there since the blower resistor does essentially the same thing.
The way the system is put together, if there was no flap, then you would have air flowing out of the heater anytime the vehicle is moving. Fan on, or not.
Note the “vent” scenario I mentioned earlier.
And if your heater control valve under the hood was not fully stopping the flow of coolant, that air coming out of the heater system when the vehicle is moving, would always be hot. Summertime or not.
Why would it need to be modulated, when it's controlled by blower speed?
With the door closed, the fan doesn’t really do much. If anything.
And pulling the TEMP knob will have exactly zero effect on the air temperature, unless the valve is open, to some degree. And that degree of opening directly affects the temperature, so we have redundancy again.
Pulling the temp knob all the way out lets coolant flow through the heater core relatively unrestricted.
With the door flapper closed none of that heat flows out of the heater. It still heats up the area around the core, eventually being felt inside the passenger compartment. But it’s not due to airflow.
Just radiant heat.
But it doesn't mix anything, unless there's a way for air to bypass the heater core and still be pulled through the blower.
Correct. It doesn’t really mix in the usual sense.
Outside air is flowing, or trying to flow through the hood vent, through the kick panel hose, into the heater core and the fan area.
It is essentially stopped at the damper door and is only allowed to actually flow through and out of either the heater or defroster duct when the flapper door is open.
Partially open, lets a little flow through, and more open lets more flow through.
Fan operating, or not. If the damper door is open, at least a little, and the vehicle is moving, you have air flowing through the heater system. The fan is only there to make that air velocity/volume greater than the natural flow coming through the hood vent.
Especially handy when the vehicle is sitting still, but since the natural air flow is not that powerful anyway, the fan greatly strengthens that flow.
Whether the air flowing through is heated by the heater core or not, depends entirely on how far out the TEMP knob is pulled and how far the heater control valve is opened.
Yeah, but what exactly does the FLAP control? That's why I was hoping for pics or a better diagram of the blower box. No one has pics of one out of the truck and taken apart?
It only controls airflow from one side of the Plenum to the other. On one side of the door is the motor and heater core. On the other side are the air outlets either for the heater towards the floor or defrost towards the window.
Along those lines, how far out you pull the defrost knob dictates whether all of the air goes one way, or the other, or only part of it.
You can pull it out halfway and have both the defroster and heater working.
I guess that’s the 60s version of a blend door?
I’m pretty sure there have been some good assembly pics taken over the years here. But I’ve never kept any handy.
Hopefully someone will have them archived.
