73-87 Square Body NON-AC Heater Box Question

[tc68bird]

Hello All,

I'm a rebuilder and I've been trying to find out the reason for two different style non-ac heater boxes.

1. Does anyone know what the additional door is for?
2. Does anyone know what years each were installed on?

Any help would be greatly appreciated.

- The first has only ONE doors (see images below):

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- The second one has TWO doors (see images below):

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[squaredeal91]

I've never seen a non a/c box like that. Im assuming one is oem non a/c and the other is converting an a/c truck to non a/c if that makes sense.

 

[tc68bird]

Really. These are the only style non-AC heater boxes I’ve seen for 73 to 87. Just trying to figure out the difference with the two and the interchange.

 

[squaredeal91]

Someone on here probably knows what the true answer is. Does it give dimensions and length? Because the firewall vent holes on firewall are in different places depending on a/c or non a/c truck.

 

[CorvairGeek]

Just a guess and I noticed the OP's location. The second style is what I imagine would be needed when aftermarket A/C is added. There would be a way needed to shut off the constant flow of fresh air that these were designed to have. Otherwise, the recirculation only A/C system would constantly be fighting a constant flow of outside (hot humid) air flowing straight into the cab (the reason the driver's side floor vent in not present with factory A/C).

 

[tc68bird]

You are correct in that the firewall is different from AC to non-AC, but these boxes are both stuck non-AC boxes with no modifications. I come across the style with two doors much more often.

Tom

 

[legopnuematic]

Looks like there were some changes in 79-80-81 per the parts catalog.

My 79, non ac, has three cables/doors. Friends 75 non ac blazer also was three cables/doors.

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