Warmer air at A/C ducts

[randy500]

Isn't it clear from the vacuum diagram that there is one vacuum switch that when activated does the following:
1. Shuts off the heater hot water flow to the heater core
2. Opens the vent on the passenger side
3. Closes the cowl vent

All of that happens at once, the cowl closes to allow air to be recirculated from the inside passenger vent that has now opened giving recirculated air to be cooled by the evaporator.

[randy500]

Now if the cowl vent is open because of binding, poor seal or a bad vacuum motor and the passenger vent is open you will be getting outside air going through the evaporator which isn't a problem, its just less cooling of the air because the air entered at a higher temperature.
The problem is the pass vent is open allowing uncooled air to enter the cabin, when sitting not much air if any will enter but when driving it will be blowing in full force. The A/C vents should still be blowing cold though just not as cold as possible because they are drawing outside air across the evaporator.

[Stocker]

Originally Posted by randy500

Isn't it clear from the vacuum diagram that there is one vacuum switch that when activated does the following:
1. Shuts off the heater hot water flow to the heater core
2. Opens the vent on the passenger side
3. Closes the cowl vent

All of that happens at once, the cowl closes to allow air to be recirculated from the inside passenger vent that has now opened giving recirculated air to be cooled by the evaporator.

Yes, the diagram makes it crystal clear. My earlier confusion was a result of not having the diagram in front of me.

[Stocker]

Originally Posted by randy500

Now if the cowl vent is open because of binding, poor seal or a bad vacuum motor and the passenger vent is open you will be getting outside air going through the evaporator which isn't a problem, its just less cooling of the air because the air entered at a higher temperature.
The problem is the pass vent is open allowing uncooled air to enter the cabin, when sitting not much air if any will enter but when driving it will be blowing in full force. The A/C vents should still be blowing cold though just not as cold as possible because they are drawing outside air across the evaporator.

The vacuum actuators appear to be functioning properly..... have not been able to verify operation or sealing of the cowl vent as it seems to be buried out of sight. Wishing now I had a factory manual but have thus far never needed one....

Nearly all testing has been done in the carport, not driving.... and warmer air is coming out of the vents, suggesting no problem with the pass. vent.

[Stocker]

Originally Posted by randy500

I think you could remove the outside evaporator cover on the engine side to clean that out and then move the evaporator to the side to clean the other side. I think that would work without a recharge, haven't tried it though,

I can verify that does work! I was able to clean out decades worth of old leaf clutter. Mostly lying on the bottom, but some was partially blocking the evaporator. Cover gaskets were harder than.... well, they were hard enough to crumble when the evap cover was opened. Hope I can find new gaskets for it....

Gonna see what I can learn about the blend door next, the remove the cowl and see about the cowl vent. I might try to seal it off like Andy did with his, unless there's a good reason to keep it working.

[DarkMonohue]

Originally Posted by Stocker

Gonna see what I can learn about the blend door next, the remove the cowl and see about the cowl vent. I might try to seal it off like Andy did with his, unless there's a good reason to keep it working.

That's the fresh air inlet for the system. If you seal it off, the only source of air to the blower motor will be the interior of the truck. Effectively, you'll always be recirculating air, and the defogger won't work very well.

[Andy4639]

Even if the truck is sitting and the cowl vent is not shut all the way it will draw hot air into the system.
The point of the cowl vent is to let outside air into the cab when the AC is on.
To blend into the cold air inside the cab for fresh out side air. With it sealed the outside air can't get in weather moving are stopped.


I'm still not sure the flapper door is correct though from what you say.
The heater core is inside the cab under the dash. The evaporator is on the motor side of the fire wall. So why if the flappers are all working is the heater core 33* it shouldn't have that cold of air inside the heater core box inside the cab. The air should be going straight through the vents and out through the vents.

[Stocker]

As always, thanks for the input. Andy, I only considered sealing the cowl vent because I thought you said you had sealed yours and all was good. Sounds like I want to have it working, though. More about that in a minute.

Andy, you know a lot more about this stuff than I do... all I know is what I am observing over the past several days, and I don't know the correct name for all the parts. Yes, the heater box is in the cab and the evap is on the other side of the firewall. What I'm seeing is cold air flowing out the the evap chamber, through the firewall, into the heater box and then directed to the A/C vents. Hope that makes sense....

Originally Posted by Andy4639

Even if the truck is sitting and the cowl vent is not shut all the way it will draw hot air into the system.

About that cowl vent. There isn't one! The vacuum actuator works, but inside the cowl there is only a 7/8" diameter plastic disc with one side broken off. I'm betting a flapper valve used to be there.... but not anymore. I wonder if this missing cowl vent has been the source of the problem right from the beginning.

[CUSTOM/10]

This is the cowl vent damper. If you don't have one & this opening isn't blocked
off, you will be sucking in outside air !

If you could post a pic of what your talking about, 7/8 plastic disk and part broken off, it would also help.

Gary

[CUSTOM/10]

One more pic.

[Stocker]

Gary, you just described it to a T, and thanks for the pics! It's not there. How something like that could go AWOL is beyond me. Gotta find one, so far the couple vendors I checked do not list it. Same with gaskets for the evaporator box. I'll keep looking, somebody has to sell them.

[CUSTOM/10]

You could test it by stuffing this opening with rags, but your cowl would have to be off to get in there.

These are sold aftermarket, the one in my pic is aftermarket, but I don't recall who I got it from. Keep looking, you'll find one.
I had to make a new pivot point for mine because the plastic pivot peace isn't repoped !
Gary

[Stocker]

Originally Posted by CUSTOM/10

You could test it by stuffing this opening with rags, but your cowl would have to be off to get in there.

These are sold aftermarket, the one in my pic is aftermarket, but I don't recall who I got it from. Keep looking, you'll find one.
I had to make a new pivot point for mine because the plastic pivot peace isn't repoped !
Gary

Good idea about using rags, and the cowl is off.... but testing will have to wait b/c the evap cover is apart and I'll need gaskets before re-assembly. Or I might get some gasket maker from NAPA and make 'em myself.

[DarkMonohue]

Originally Posted by Stocker

Good idea about using rags, and the cowl is off.... but testing will have to wait b/c the evap cover is apart and I'll need gaskets before re-assembly. Or I might get some gasket maker from NAPA and make 'em myself.

I would love to see some pictures showing how far apart you are able to get it without disconnecting the system or removing major body parts (yours or the truck's).

Maybe one of F.A.A.benny's threads has something to say about sealing up the evaporator housing. No doubt you could fake it, but the "quality" of some of the consumer-grade products retailers sell these days might make it a risky proposition.

[Stocker]

Originally Posted by DarkMonohue

I would love to see some pictures showing how far apart you are able to get it without disconnecting the system or removing major body parts (yours or the truck's).

Maybe one of F.A.A.benny's threads has something to say about sealing up the evaporator housing. No doubt you could fake it, but the "quality" of some of the consumer-grade products retailers sell these days might make it a risky proposition.

Last time I checked, between a dead battery in your Mom's camera and our lack of computer skills, it wasn't happening. Not much to see anyway.... I removed the engine side of the evap cover, then removed a couple small clamps from the AC hard lines to facilitate moving the evap core towards the engine so I could clean debris from the fender side.

I had intended to ask what type of "form-a-gasket" might work well, if any. No luck yet finding any proper gaskets through the usual vendors. If I can't find something useful in F.A.A.benny's threads, I'll try contacting him.

[DarkMonohue]

Hey, that's actually pretty great that you could break it down that far without removing the hoses etc from the evaporator. And it actually sounds like you might, fingers crossed, be able to remove the other (outboard) side off the truck now. At that point you could either cheat a little and snake the blend door out, or just drill the rivets out and break it all the way down, replace the gaskets, and stab it back in, knowing it's all as correct as it can get.

[Andy4639]

Well my truck has had the cowl flapper gone for say 10-15 years now. It's fine it defrost as good as it ever did. If you need fresh air I open the drivers side kick panel are open a window no biggie! My truck get's cold down to 38* even when it's in the mid 90 outside here.

[DarkMonohue]

If you are on the fence about removing the evaporator box outright, these threads may help you make the decision. They're on non-A/C trucks, but the procedure they follow for removing their heater boxes should be about the same as removing the evaporator case from an A/C truck.

http://67-72chevytrucks.com/vboard/s...d.php?t=600448
http://67-72chevytrucks.com/vboard/s...ad.php?t=69812

In for a penny, in for a pound. But that's easy to say when it's not my time, money, or skinned knuckles at stake.

[tdangle]

The Truck and Car Shop in Orange , CA has the gaskets, new flapper doors, etc. Check it out truckandcarshop.com they have an online catalog. I bought my stuff there, luckily local for me so no shipping costs.

[Stocker]

Time for an update if anyone is interested. Got everything re-assembled today without too much bloodshed, though I may have taught myself a few new words.... no small feat after decades in construction. A quick reminder so you don't have to re-read the entire thread: before teardown I read as low as 33 degrees inside the heater box but could not get lower than 60-62 at the outlet vents in the cab. Outside temp was high eighties.

I removed the engine side of the evaporator housing and cleaned out some leaf clutter, most of which was lying on the bottom but some was on the evap core so I cleaned that off too. Then I checked the cowl vent, only to discover there was not one. After re-assembly I stuffed the right end of the cowl full of rags to block airflow and simulate a closed vent damper. Time for a test. Ambient temp was 94 degrees and after a short time running, I got 40 at both the heater box and at the vents in the cab, and as low as 38 for a few moments.

This little project has had it hiccups, some my fault, some the shop that did the install, and some with defective parts (both old & new). There are still a couple things to take care of but I am finally satisfied that I will have a proper functioning A/C system again. "Thank You!" to all who have helped with advice and encouragement. This forum is an invaluable resource because of its great members.

[F.A.A.benny]

Good deal.

[Andy4639]

Glad you got it.It's great place to know there are so many people willing to help. It may seem we get a little up set sometimes but in the end we all are here for one reason. We love our trucks!

[DarkMonohue]

Thanks for the update. I am really glad to hear you got it working like it should. Once you get the phantom recirc damper in place in the cowl it'll be better than ever.

Be careful, though. Get it too gussied up and you won't want to get it dirty. You'll have to resort to buying artisan-cut, sustainably-harvested heirloom firewood from some website featuring shiny people in matching sweaters, scarves, gloves, and hats frolicking in the snow with their sweater-wearing golden retriever...

[Stocker]

Originally Posted by DarkMonohue

Be careful, though. Get it too gussied up and you won't want to get it dirty. You'll have to resort to buying artisan-cut, sustainably-harvested heirloom firewood from some website featuring shiny people in matching sweaters, scarves, gloves, and hats frolicking in the snow with their sweater-wearing golden retriever...

Hah! You know me a lot better than that! When I was talking to Nate's friend about painting it, I told him it would still be a working truck, just like always.
Nate told him within a year it will have brush scratches down both sides.

[dmjlambert]

Originally Posted by DarkMonohue

Thanks for the update. I am really glad to hear you got it working like it should. Once you get the phantom recirc damper in place in the cowl it'll be better than ever.

I've been reading this thread with great interest. By phantom record damper in place do you mean just block the hole so it is shut all the time? Is that what DarkMonohue and Andy4639 have done? Am I correct in that permanently sets the A/C to recirculate the air, what most cars call Max A/C setting?

I've always wanted to eliminate outside air and always recirculate. Here in the city, there is no good air outside anyway. All there is to breath in traffic around here is stinking diesel exhaust fumes from some car ahead of me, and I hate when that stuff is drawn forcefully into the car and into my face by an air conditioner. If I want outside air, I'll roll down a window.