Fan blower issue

[DeepC73]

Hey guys,
I have looked everywhere for a solution or similar issue. I just put my heater box back in my 73. The PO removed it 15 years ago and sealed up the firewall holes. I have it in and it is working. However, I only feel air if the center fan knob is pulled (pull for heat). If I push it in, there is no air coming out, even though fan is moving. What simple thing am I missing?

 

[DirtDonk]

Just the fact that closing the damper door reduces the amount of air that the fan has available to push through the rest of the plenum.
If you "Pull For Heat" and leave the "TEMP" knob all the way in, the theory is that you will only get cool air coming through. However since there is always some heat in the core it seems, cool air is a misnomer!

I'm pretty sure that's how mine used to work. Right now I'm driving around with a Vintage Air setup that is completely different. I like the simplicity of the stock setup, but love having A/C even more!

Paul

 

[DirtDonk]

By the way, that same pull-for-heat thing is basically a vent to let outside air into the cabin as well.
Even without the fan blowing, if you pull the knob out you will get air flow through the system as soon as the vehicle is moving. I used to use that a lot out here in my mild climate. Most of the year I only needed some air flow, but not much modification of the temperature or flow.

Paul

 

[DeepC73]

So the defrost pull opens and closes the defrost damper. What does the pull for heat damper actually do mechanically?

 

[DirtDonk]

They both manipulate damper doors. The heat/defrost simply moves the diverter door from one flow path to another within the plenum, but the pull-for-heat damper door literally opens up or closes off the inflow of air into the plenum from the passenger side kick panel through the hose.

 

[DeepC73]

Good to know. I suspected that. When the heat damper pull is closed, where is it pulling air from?

 

[EPB72]

Good to know. I suspected that. When the heat damper pull is closed, where is it pulling air from?

the inlet is on the far right,through the right side hood vent, down right side inner fender ,through kick panel, into cab with the bellows tube hooked up properly it will be all fresh air to heater box and only fresh air...all that air passes through heater core ...

the heater core can be either hot or cooler depending on temp knob postion [control valve underhood stops coolant flow to core if works properly]

both dampers on the outlet side of heater core one I;d say is really a defrost/floor door....the other just closes off air flow through the plenum 90% maybe..

 

[Rustytruck]

all assuming you got the foam sealing kit to rebuild the box. after 50 years the sealing foam inside is shot or gone. if you have to replace the diverter valve get the new style made of black plastic they work so much better than the factory type metal ones. much easier to open and close.

 

[DirtDonk]

When the heat damper pull is closed, where is it pulling air from?

Short answer, it isn't.
What I was trying to describe before is that when the main damper door is closed the fan can't pull any decent volume of air in from anywhere. I'm sure it gets some backwards from the registers, but it's actually trying to push air out with nowhere to pull from.
This is why unless you pull-for-heat, you don't get any air flow to write home about.

Paul

 

[DeepC73]

Thank you all for the help and comments. Now I understand.