Heater core housing help please

[shanespurlock]

So I have a 1973 CJ5 . When I bought it the heater core was leaking. I removed the heater core box and it was full of leaves, a hornets nest, etc. I got it all cleaned out and replaced the heater core.

However, the flapper door that directs air to either the floor or defrost...even in full defrost mode (I even disconnected the cable and moved the control arm by hand to make sure it was going fully in the proper direction) there is only a slight amount of air coming through the defrost vents, and a lot of air going through the floor vents.

Anyone else have this issue? Any known fixes?

I also notice that all the online images for this heater box show one oval shaped port with an oval hose going up to the plenum that attaches under the windshield, however my heater box has two round ports. There is one that had nothing attached, so i taped it off, and the other round port had a round hose going to the defroster plenum. I was thinking that since there was a second port there would be a second plenum, but there doesn't appear to be. Seems odd.

Any help is greatly appreciated. thanks in advance.
---Shane

 

[Posi]

You should only have 1 hose going to the defroster nozzle.
Check the hose for rips/holes, dirt/debris.
The defrost never did work well from the factory, even in the later CJ's.

 

[shanespurlock]

Any idea what the other port is for? Ive seen it in some diagrams online but now that Im looking for them, of course I can't find them. Go figure. Is that flapper door supposed to have some kind of seal on it? Cant figure out why its sending so much air to the floor vents when in full defrost mode.

 

[HackFabrication]

Any idea what the other port is for?

It's to direct air up to the fresh air plenum to melt snow/ice, which then can drain out through the firewall via the hose. A lot of people have capped it off.

I've never look at any of the AMC automobiles or J trucks, but it wouldn't surprise me if they used the same heater box in another vehicle. AMC was good at 'maximizing part utilization'....

Is that flapper door supposed to have some kind of seal on it? Cant figure out why its sending so much air to the floor vents when in full defrost mode.

Most of the foam has probably deteriorated inside your heater box. When I re-did my 76 box (it is similar to yours), I had to get creative with finding foam.

And as was already posted: They never were know for having stellar defrost systems. Design issues with how the air is vented up into the window frame and out. Not real effective.

 

[Posi]

The heater/defrost in your CJ came with two outlets from the factory and the empty hole is as Hack mentioned.

The FSJ's had one large hole with a cap, that cap had two holes that fed the two defroster nozzles.

As I mentioned previously, I would check the hose for rips or debris. Often times there isn't a clean seal between the hose and defroster nozzle, other times they can get dislodged especially if there has been some wiring work behind the dash.