72 A/C K20 no defrost help request
 

My new K20 heater blows hot air like mad, but only out of the center bar in the dash above the radio. Virtually none out of any other outlet no matter what I do with the levers on the heater control panel. I have seen a couple other threads referencing possible vacuum line problem or a broken flapper/diverter door, but looking for help and clarification on this. The cable from the defrost lever is disconnected on the heater box from the diverter lever that it attaches to as if the PO were troubleshooting the problem. That lever works by hand, and feels and sounds as if the flapper door is moving properly in there. Is this the diverter that I am supposed to be looking at?

Attachment 1490856

or something else?
Attachment 1490857

I looked under the hood for a 3 position vacuum port where something might be disconnected but not seeing it or don't know where to look.

Attachment 1490858
Attachment 1490859
Any help or advice appreciated.

and, just because :chevy:
Attachment 1490876

Re: 72 A/C K20 no defrost help request
 

Most likely the flap in the diverter box is broken - basically, they all break.
This box is to the right of the one in your picture and is controlled by the "outlets" lever on your control; it sends the air either to the upper vents or the foot/defroster outlets. Take off the heater outlet box and then the S-shaped duct to the right, and you should be able to see or feel inside the diverter box if the flap is moving.

Re: 72 A/C K20 no defrost help request
 

The diverter you pictured controls the air flow to the defroster vents/floor.the other diverter that controls the air flow to the center and outer vents is up stream from the one pictured, and the cable that actuates it, attaches from behind it, so it's out of view.chances are, the flapper in that diverter has either a broken arm that the cable attaches too, or the flapper itself has broken.
With regards to the vacuum hose issue, there is a vacuum fitting on the back of the intake ( at least on a stock intake) that is close to the distributor, the vacuum hose then goes to your vacuum cannister /reservoir,which, from the pictures you have posted, is missing,you can get by without it, but the doors will be sluggish to open or close, because the vacuum reservoir stores vacuum to aid in opening these actuators. the hose then routes through the firewall to the defrost control panel, then it tee's off to the vacuum actuators on both the cowl vent door, and the recirc door below the glove box and the water control valve on the heater hoses.
Hth,
Ben

Re: 72 A/C K20 no defrost help request
 

Ok lets see if this helps.
In the picture I posted the far left is defrost outlets. The next section is just a piece of plastic, is no more than a union if you will, then the next piece is the diverter that you need to check and see it it's working. This piece directs the air to the sides and center vents for AC. I would suggest taking the other pieces off and seeing if it's working.



http://i1233.photobucket.com/albums/...9801DADABF.jpg


Now for the vacuum lines you need a port off the engine which in your picture I don't see. It will tie to the vacuum resevoir in the picture that should be mounted on the box under the hood which like I said I don't see it.
The vacuum control head should be on the controller in the dash.

http://i1233.photobucket.com/albums/...ecs/Vacuum.jpg

Re: 72 A/C K20 no defrost help request
 

Wow, guys, thanks. Again I am humbled by the nature and helpfulness of people on here. Thats a lot of info to work with, I should be able to get started with that. I looked again at the pic of the engine compartment and annotated it below with a couple questions. Is the vac canister available aftermarket?

Attachment 1491033

Re: 72 A/C K20 no defrost help request
 

The hose coming off the engine looks to be the right one. That bracket isn't anything I've ever seen. You can buy the vacuum canister new are find one off any GM vehicle with AC. They may look a little different are mount different but should work.
The black ball thing on the side of the AC housing is what it should look like.:chevy:



http://67-72chevytrucks.com/vboard/a...1&d=1453645545

Re: 72 A/C K20 no defrost help request
 

OK, thanks Andy! BTW, your engine compartment sure looks nice.

Re: 72 A/C K20 no defrost help request
 

That hose off the intake hooks up to the vac ball, if it I open ended then you have a vacuum leak. The other port on the vac canister goes to the heater control. The vac canister and diverter box are available. I just got a diverter box from gmpartsdirect.com (I think I'll have to look I have the #) for 80 bucks

Re: 72 A/C K20 no defrost help request
 

Thanks. That picture was taken while the motor was being installed.:chevy:

Re: 72 A/C K20 no defrost help request
 

Ok, thanks HDFF. I just went out and took the small vac line that is coming out of the firewall and assumed it was the one that goes to the heater control and stuffed it right into the intake vac line that was indeed an open vac source, smoothed out the idle if nothing else, and tried it to see of it would divert to defrost. It did a little, maybe, or it is my imagination. I may have had a tiny bit of flow to begin with, so not sure. Not a lot, so that flapper may not be moving much if it is at all. I will look for that vac canister and diverter box in case I need it, if you come up with part number or link before I do thanks in advance.

Re: 72 A/C K20 no defrost help request
 

Gmpartsdirect.com
P/n 3891276. Ac diverter box

Re: 72 A/C K20 no defrost help request
 

Ok, a little update to the thread. I repaired my flapper, bought and installed a vac canister, installed all new ductwork, and a new s-duct, and almost finished putting everything all together (with a new refurbished tach cluster :metal:).
But I am not sure if I am missing something because the s-duct to floor vent/defrost box connection is looser than a goose. In fact, the whole thing is sloppy. The flapper box connection to the firewall box is screwed together, but not confidence inspiring tight. The s-duct is screwed on there, and then the floor/defrost box, and I feel as if I am relying on the bolt that goes through the firewall to hold the floor/defrost box to hold everything together, and it does a very poor job of it. I am starting to understand why the PO had a load of duct tape around everything. Not what I was hoping for. Here is a picture of the s-duct connection and everything together. It looks like it doesn't go in far enough to screw together as I can see the holes in the metal of the floor vent box and it is bottomed out. I flipped the s-duct around to make sure I had it on the right way and this ended up like it made more sense, but I could be wrong. What am I missing?
Attachment 1508734