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Discussion Starter #1 (Edited)
This thread covers restoration of my original RHD heater box. I believe NAS heater boxes work in an identical manner.

I'll jump ahead to some diagrams showing how the internals of the heater box work, for informational purposes.

There are two internal flaps which control the routing of the air in the heater box.

The vertical flap controls whether the air flows through or around the heater core.

The horizontal flap controls how much of the air flows out of the heater box. The blower motor on the heater only has two speeds:
1. full blast
2. imperceptibly slow

I believe this is used as a primitive form of fine velocity control on the heater box when operating in full blast mode.

The heater box was acid dipped, bead blasted, and then powdercoated in BBS Gold.
 

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Always wondered what happened in the black box!
 

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What is really cool about the heater design is that it can be flip-flopped to work on either side. My guess is after the pieces were stamped out of sheet steel it would be folded/bent/pop rivet/spot welded a certain way depending on if it was being made for a LHD or RHD vehicle. The blower fan housing is specific left to right tho.

Also - there is a different heater core design and probably a change in the box as well. Not sure what year they went from the down in/outlets to the horizontals in/outlets.

And those added graphics are sweet sonoronos!
 

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Discussion Starter #5
Installed the replacement gm fan.

All old part numbers listed on the web seemed to fail to find a part at autozone, Napa, advance, etc.

New part is interchange for a 1994 Buick Century, V6. Attached is the part I got from advance auto parts.

The rest of the install instructions are identical to that provided in the thread where lav did his heater upgrade.

ForumRunner_20151004_055914.png
 

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Discussion Starter #6
Heater box vent flap foam used is 1/4" heat-resistant EPDM 2.5psi closed-cell foam, with a 215 degree maximum temperature.

I recommend anyone else replacing the vent flap foam to use 1/8" foam in the future.
 

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The horizontal flap controls how much of the air flows out of the heater box. The blower motor on the heater only has two speeds:
1. full blast
2. imperceptibly slow

I believe this is used as a primitive form of fine velocity control on the heater box when operating in full blast mode.
I assumed it was you close off the flow when you don't want air from the outside, like when wading, or it is hot out.

At least on mine, I thought the speeds were well chosen. About 50% of the heat output and air flow on the low speed. 78 cfm low speed, 149 cfm high speed.
 

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Mine does not blow at all, I suppose I will start checking. I suppose I start with see if the fan is turning freely then electricity gets to it?

Thanks for sharing this.
 

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Discussion Starter #9
Its possible. One strange thing is that it doesnt actually appear to be physically possible for the horizontal flap to close completely using the push-pull cable.

So whatever the purpose of the flap is, it has to do it always partially or fully open.

Out of curiosity, do puma trucks even have a heater box? Or is it for an ac evaporator only?
 

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It should close fully. Mine did.
 

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Out of curiosity, do puma trucks even have a heater box? Or is it for an ac evaporator only?
Blower is in the engine bay, heater box & A/C evap (I think) is behind the centre console. That's why it sticks so far into the cabin... got to pack all that stuff some where.
 

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Not Defender related but my old Jeep had a heater box that once it is bolted in, it changes the dimension of the box ever so slightly the operation of the blend door became rather snug.
 

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Discussion Starter #17 (Edited)
I received some questions regarding the GM fan upgrade, and really this thread has the most information on the topic - courtesy of Nathanwind:

http://www.defendersource.com/forum/f6/heater-fan-upgrade-in-the-nas-d-90-a-38561.html

I think the only things I can add are:

1. The GM blower motor comes with a LHD blower cage. If you have a RHD truck, save your original RHD blower cage.

2. The GM blower motor is wired for LHD blower operation. If you have a RHD truck, you must reverse the wires to reverse the direction of the blower motor.

3. You must open the motor on the GM blower by drilling out 3 rivets.

4. You must remove the ground wire riveted onto the blower motor housing.

5. You must hammer flat the raised lip around the periphery of the blower motor housing.

6. You must drill at least one new hole in the periphery to allow the GM blower motor housing to bolt to the Defender fan box.
 

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Heater control cables?

OK, so this is a dumb question, but I have a loose cable on top of my heater box. I have an 88 LR90 NAD. The hot/cold cable seems to be connected to the top of the heater box and works fine. The windshield/floor director control also seems to be fine. Airflow seems to have two fan speeds: slow and fast. What should this other cable connect? It seems to be actuated by the fan speed cable.....:confused
 

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Discussion Starter #20
Whatba timely thread revival, where did you source the heater core Sonoros? Any recommendation? RHD it has the turnes down heater core pipes.
Sorry I never got back to you, Michael. I never got a notice that you asked a question on the thread, and I apologize.

I sourced the heater core from Rovahfarm, part number AAP817.
 
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