Defroster Vent Question.

[Ludigdrums]

Hello all!!!

Well, I just got done replacing my A/C Heater control and diagnosing a vacuum problem in my '81. It turned out to be the Plenum, which is in the passengers side fender. There's a vacuum line going to the front of it, but when you take it out, there's another one on the back which you cannot see. Mine was disconnected, preventing me from getting the proper A/C selector settings.

Anywho, I noticed while doing this that the vent that goes to the defroster doesn't really make contact with the lower assembly that feeds it air. Is this correct? It seems weird to me....as if it's missing a piece or not aligned properly. However, I cannot see how it could be aligned any other way.

I can't seem to find anything in my assembly manual or shop manual. It looks as though the diagrams just go into one another.

Any thoughts?

Thanks!

- Jeremy

 

[Art Jett]

Mine was the same way on my 77! I just used some of the metal tape used on residential air conditioning ductwork. It is available at Lowes or Home depot. It isn't expensive and it is extremely sticky. I wrapped about 3-4 layers around the ducts and it worked great!

 

[Bob Chadwick]

Mine didn't either and I just duct taped the two pieces together. I think I read that there was a foam piece there originally that deteriorates over time.

 

[JohnZ]

The gap between the heater-A/C case defroster outlet and the upper defroster duct that attaches to the upper instrument panel is there by design; all GM cars are done that way on purpose so the blower noise and vibration from the main heater-A/C case doesn't get transmitted directly to the upper duct, which would result in the noise/vibration being amplified by the instrument panel (like a drumhead). The gap is supposed to be there.

 

[Ludigdrums]

Ahhh ha...thanks to all for your replies! Like Bob and Art, I too was thinking of sealing it up. Thanks for the confirmation, John, that the gap is supposed to be there.

I'm still having an issue with getting the correct settings. It's definitely a vacuum issue because when I increased the vacuum (by bypassing the headlamp hoses) everything worked excellent and switched modes real fast. I'm only getting 6 PSI to my heater control, but ~20-22 from the manifold. I know something is drawing from the headlamp hoses.

Does anyone know what the correct vacuum readings should be. I know everyone's engine is different....but at least an acceptable amount of loss from the manifold to the heater/headlamp/etc.?

I checked the little check valve from the manifold that splits 1 into 2. I think I need a new one of those because it seems that I can blow both ways when it should only allow one way flow.

Am I on the right track here? Any help is as always most appreciated!

Thanks!

- Jeremy

 

[Bob Chadwick]

There's a filter and a check valve. Things seemed to work better when I replaced both of them.

 

[jdp6000]

Its not a one way. Its there to trap any oil or crud that may escape from the engine.

The vacuum part operates the ports tha direct the heat/cool air to the various vents. Thats the upper control on your switch. It also contols the cut off valve on one of the heater core hoses (upper passengerside) I think.

The lower that says hot/cold is not vacuum operated its cable operated. The cable opens and closes a flap in the heater core box. Which allows hot air or cold air in. There is a tension control on the line which can be accessed by removing the passengerside consol panel.

Jim

 

[NewVetter]

Hi guys. I have an 82 and assume vent stuff is same as Ludig's 81. I have AC and unwanted heat issues right now, (AND vacuum probs, haha).
1) I think I just need an AC recharge for AC issue cuz when flip AC sw on, can see/hear engine kick down and Alt move a tad but no cold AC.

2) I have unwanted heat on drv side around knee area. I was under there yest and saw a 'canister' at pass. side right behind coutesy light on kick panel. Is that the plenum you spoke of Ludig?

Basically, I'm trying to figure out why warm in drv side. Is it most likely cuz some vent flap not closing ala plenum/htr core related, or could it be actual vent ducts separated under dash? Thx for any info when get time. Regards.

 

[Ludigdrums]

Bob, for some reason I don't have the filter...but I will go get a new one along with the valve and see what happens. I still think it might be my vac canister in the front not holding vac.

Jim, thanks...I was going by something else I read which seemed to make sense. That is that it had to be a 1 way in order to not let the vacuum come back when the engine is off. For instance, once I shut my car off, I cannot do anything with the headlights. Supposedly, if everything's working correctly, you should be able to pop the headlights up even after the car is shut off. Also, thanks for the explantion of the other systems, but that I know is all correct as I just went through it all.

NewVetter, No, that canister is for the kick panel vent. The plenum vent is on the outside of the car just above the kick one. You have to pull back the screen in the fender to access it. As far as the heat...it could be many many things. As far as vacuum is concerned, one of the small vac lines goes through the firewall to a water shut of which will prevent the heater core from heating up. But that also relies on your temperature switch being adjusted correctly so that it engages the water shut off switch. You can see all this better if you remove the glove box. Good luck.

Thanks as always and keep 'em coming!

- Jeremy

 

[jdp6000]

Hi guys. I have an 82 and assume vent stuff is same as Ludig's 81. I have AC and unwanted heat issues right now, (AND vacuum probs, haha).
1) I think I just need an AC recharge for AC issue cuz when flip AC sw on, can see/hear engine kick down and Alt move a tad but no cold AC.

2) I have unwanted heat on drv side around knee area. I was under there yest and saw a 'canister' at pass. side right behind coutesy light on kick panel. Is that the plenum you spoke of Ludig?

Basically, I'm trying to figure out why warm in drv side. Is it most likely cuz some vent flap not closing ala plenum/htr core related, or could it be actual vent ducts separated under dash? Thx for any info when get time. Regards.

First with the A/C on feel one of the pipes coming from the the compressor. It sould be cold.

Second feel the hose that goes to the shut off valve (near the passengerside rear of the engine)...should be a temp difference on one side if its working.

Third, make sure the flap in the core box is closing. It blocks of the chamber that has the core in it...this is what generates heat. By moving the switch from hot to cold you should notice a difference. Sometimes the door in there does not close completely or not at all. The cable running from your switch to the box is adjustible. There is also a vacuum controlled flap in there that controls the distirbution. Easiest way to check is to remove the glove box and see if the cable is moving the flap.

You may also need a recharge.

Jim

 

[NewVetter]

more dash/ductwork Q:s

Hi guys, speaking of duct work... just got my 1982 gauge bezel out so as to see all ductwork. In behind is a black 'box' that can be seen, when I remove the front duct that goes to the vents just above the gauges. It's the box that also has the Cold / Hot lever cable going to the top of it. Left of that and lower, is a metal door shaped literally like the state of Nevada, haha in that I can push on and it opens toward the firewall, pivoting on the left side. It has a white-ish teflon looking piece attached to it that has a very small aluminum pin as part of it. What makes this door open? I mean, there is no cable going to it. Just want to make sure I'm not missing a part or something when I put it together again. I get the feeling that something mechanical is supposed to open this door. Might I be missing a part or something? Also I saw another one of those vacuum canisters, like the one at pass side kick panel area. This one though is up in behind the tach. Any idea what that one does? Answer if get time.... Regards

 

[gmjunkie]

First with the A/C on feel one of the pipes coming from the the compressor. It sould be cold.

Second feel the hose that goes to the shut off valve (near the passengerside rear of the engine)...should be a temp difference on one side if its working.

Third, make sure the flap in the core box is closing. It blocks of the chamber that has the core in it...this is what generates heat. By moving the switch from hot to cold you should notice a difference. Sometimes the door in there does not close completely or not at all. The cable running from your switch to the box is adjustible. There is also a vacuum controlled flap in there that controls the distirbution. Easiest way to check is to remove the glove box and see if the cable is moving the flap.

You may also need a recharge.

Jim

I agree 100%, and some times they just get leaves and other debrie in them!!! And also I have seen evaporator cores get lint,hair,leaves, gum wrapers, just crap in gen. in them and can't circulate through it!!