Inner Cab Heater/AC Housing Reference Pics

[HotRodPC]

I'll answer one of the questions for you right away. On the passenger side air dampner, Yes, you can manuallly close that off. If it's an AC truck its not controlled by the Vac diaphram. You could even swap that vent door out with a NON AC heater Only truck vent door which is manual door with a lever on it and your passenger can reach down and open and close it as they wish, or you could close it and leave it closed.

 

[89Suburban]

This is the best thread and pictures I've seen on the internet! So hard to figure out how the air flows in the heating/AC system. Thanks a bunch for posting the pictures and diagrams!

My 85 K10 AC is not working and now being winter, I really need the defrost. Years ago, I changed the blower motor a few times with junkyard donations hoping to fix the lack of defrost. Now back in the cold of winter, I need defrost again.

I removed the glove box and the box behind it, attached to the main air distributor/heater box.
I zip tied the rusty door closed, by pulling the arm rod on top toward the other one with zip ties.
I disconnected the defrost door/flap rod and left the vacuum pod rod pushing against it in the position that directs air to the upper defrost conduit.
I put tape around the bad design gap between the upper defrost conduit and the lower distribution box.
I put tape over the opening where the zip tied rusty door is, just to make a tighter seal and push more air to the defrost.
I put tape over the bottom opening for the floor vents (under the vacuum actuated defrost door/flap).
I bought a new VDO Oreilly blower motor for a "1994 GMC 1500 4X4" and installed it. The previous motor had the wrong(d'oh!), "short" cage and didn't push much air.
I turned on the fan and got a huge improvement in defrost air flow!

I would like to completely close off outside air and recirculate inside air if possible to keep the hot air in the cab and odors outside. I'm assuming my vacuum pods don't work though I could be wrong. I'm still not completely sure how the air flows to/from the blower.

Is there a way to manually close the outside air damper flap/door/valve that looks like it's on the right of the passenger side foot well and has something to do with air flow with the blower motor?

I'm also planning to install an eberspacher coolant heater, but I suppose I'll have to ask about installing that in a 6.2L diesel engine forum in order to figure out the coolant flow, etc. Anyway, thanks again for a great forum, the best I've seen so far for these trucks!

Don't forget about the hidden vacuum servo and door under the wiper cowl, I think that has something to do with outside air too.

Also on your truck's doors at the rear bottom you can duct tape the cab vents closed to help keep the cab warmer.

 

[chengny]

I would like to completely close off outside air and recirculate inside air if possible to keep the hot air in the cab and odors outside.


Proper operation of the defroster requires a supply of fresh (i.e. outside) air. Blocking off the fresh air inlet will result in the humid air (the air that is inside the cab) just recirculating - the windows won't clear up.

 

[RockyGryphon]

Proper operation of the defroster requires a supply of fresh (i.e. outside) air. Blocking off the fresh air inlet will result in the humid air (the air that is inside the cab) just recirculating - the windows won't clear up.

I was wondering about that. Maybe I won't worry so much about sealing the cab, but it would be nice to be able to close off the outside air when driving by the refinery and its par'fumes. I would have to close the rust holes in the doors in addition to their vents, then operate the outside air valves...

Are there just two outside air doors/flaps/valves?

On my AC'd truck, the pictures/diagrams in this thread look like there's a flap on the passenger side foot well, and another one under the windshield wiper vent / air intake. Is that right?

Are they opened by setting the top slider on defrost?

What closes them, or do they ever close completely?

On my car, the manual showed that there was always fresh air (from my stinking engine) so I zip tied that completely closed and its defrost works fine still because the air here is so dry. Does anyone know how the air actually flows on a truck with AC?

It looks to me like there's a flap for the floor / defrost duct, two flaps that work together by vacuum servo that cut off the defrost and floor ducts, directing air to the dashboard vents, and finally, I saw the front flap toward the AC condenser that opens when the ?bottom slider is moved to ?cold. Then it becomes a mystery to me.

Does air get sucked from the windshield wiper vent, down past a vacuum servo-operated flap to the blower motor and pushed through the AC condenser, then the heater core, and finally dash or defrost?

If you set the temp to cold, do you make air bypass the heater core?

If you set both sliders to heat, does the wiper flap close off the outside, and the passenger foot well flap open to allow air to get sucked into the blower motor from the cab to make a recirculate situation, or what?

I've looked at the pictures, I've looked behind the blower motor when I had it out, tried to shove the cell phone cam in there and make sense of it, but I get lost in that dark cave. Sorry for such long posts, I'm just wanting to survive tackling this bear of a problem.

 

[chengny]

All answers are based on a truck with A/C.

Are there two outside air doors/flaps/valves?
There are 2 dampers that can allow outside air into the cab. One is operated by the control panel (the one under the cowling on the passenger side). The other is manually opened/closed (the one down by the e-brake) by pulling /pushing the rod.

On my AC'd truck, the pictures/diagrams in this thread look like there's a flap on the passenger side foot well, and another one under the windshield wiper vent / air intake. Is that right?

Yes. The one under the wiper cowling is the outside air intake damper and the one behind the shield in the passenger side kick plate is the cabin recirc damper.

Are they opened by setting the top slider on defrost?

They work opposite to each other. When the intake is open the recirc closes and the fan takes in outside air - when the fresh air inlet is closed the recirc is open and the fan takes suction from the cab through the recirc damper.

What closes them, or do they ever close completely?

They are operated by vacuum. The control panel gets a supply of negative pressure from the engine's intake manifold. The control panel then sends that signal to the various diaphragms as selected. The diaphragms are either opened by vacuum/closed by spring or opened by spring and closed by vacuum. The only one that is moved in both directions by vacuum is the diaphragm for the mode door. The recirc door also has an extra spring to ensure tight closure.

On my car, the manual showed that there was always fresh air (from my stinking engine) so I zip tied that completely closed and its defrost works fine still because the air here is so dry.

Does anyone know how the air actually flows on a truck with AC?

I do.


It looks to me like there's a flap for the defrost duct, two flaps that work together by vacuum servo that cut off the defrost and floor ducts, directing air to the dashboard vents, and finally, I saw the flap toward the AC condenser that opens when the ?bottom slider is moved to ?cold. Then it becomes a mystery to me.

You seem to understand the defrost flap. Those other two doors that work together are the blend (temperature) and mode (direction). One note: you can completely direct all air from the fan through the evap coil (and bypass the heater core) by moving the temperature lever all the way to cold. The only difference between this and MAX A/C is that the outside air damper will be open. When in MAX A/C, the outside air closes and the recirc opens.

Does air get sucked from the windshield wiper vent, down past a vacuum servo-operated flap to the blower motor and pushed through the AC condenser, then the heater core, and finally dash or defrost?

Yes, unless max AC is selected. If max A/C is selected, the air supply for the fan is taken from the cab via the recirc flap. Also all the air passes through the evap coils - none through the heater coil. If the controller is on heat, vent, bi-level - the temp is controlled by varying the amount of flow through the heater/evaporator. The cooler the temp selected, the greater volume of air is directed through the evap. Move the lever to warm and the blend door closes off some of the flow to the evap and opens more towards the heater coil.

If you set the temp to cold, do you make air bypass the heater core?

Yes but you will be cooling down incoming fresh air - unlike when in Max A/C. In MAX mode you are cooling the already cool air within the cab.

If you set both sliders to heat, does the wiper flap close off the outside, and the passenger foot well flap open to allow air to get sucked into the blower motor from the cab to make a recirculate situation, or what?

No, if either HEAT or DEFROST are selected the outside air damper is opened and the recirc closes.


Look at this diagram. It is kind of difficult to read but it does explain how the system works:

You must be registered for see images attach

 

[HotRodPC]

You bastards are going to kill yourselves driving blocking off all the outside air and breathing nothing but fuggin carbon monoxide. Gonna go nighty night cruizin down the freeway. I know form experience, sleeping, cruise control and hwy driving don't mix.

 

[chengny]

Preachin' to the choir!

 

[89Suburban]

My. Burb's PO had all 4 of the door vents duct taped closed. I can see the glue from the tape. I am figuring the heater core must have took a **** and he did that to get by until the core was replaced. I will be going to a heat only box and controls at some point.


Sent from my iPhone using Tapatalk

 

[RockyGryphon]

I'll answer one of the questions for you right away. On the passenger side air dampner, Yes, you can manuallly close that off. If it's an AC truck its not controlled by the Vac diaphram. You could even swap that vent door out with a NON AC heater Only truck vent door which is manual door with a lever on it and your passenger can reach down and open and close it as they wish, or you could close it and leave it closed.

All answers are based on a truck with A/C.

There are 2 dampers that can allow outside air into the cab. One is operated by the control panel (the one under the cowling on the passenger side). The other is manually opened/closed (the one down by the e-brake) by pulling /pushing the rod.

I've never seen anything besides the hood and brake release knobs by the emergency brake and nothing on the passenger side inside the cab. Am I missing something? Maybe I just never noticed? My 85 K10 with AC is a "Silverado" trim.​

*cut* If max A/C is selected, the air supply for the fan is taken from the cab via the recirc flap. *cut*

So normally, if you select Max A/C, and you also move the bottom slider all the way to heat, do you then recirculate heat (with the A/C running unless like mine, it doesn't)?
IF not, then is there normally no way to recirculate heat, other than to modify normal operation (zip ties and duct tape!)?​

You bastards are going to kill yourselves driving blocking off all the outside air and breathing nothing but fuggin carbon monoxide. Gonna go nighty night cruizin down the freeway. I know form experience, sleeping, cruise control and hwy driving don't mix.

Luckily my cruise control doesn't work and I usually open a window to stay awake when I get drowsy until I can pull over and take a nap on long drives. I think monoxide poisoning has been happening whenever I smell the stench of my exhaust or engine compartment coming into the cab from the outside air intake since a broken header pipe bolt was replaced with a J bolt, probably not making a good exhaust seal (but plenty of noise), not to mention the tail pipes were replaced with downspouts from the mufflers under the bed, so when the truck is stopped, smoke rises behind the windows of the cab from under the bed. I'm sure this explains why I'm already half brain dead and asleep most of the time. That must also be why I can't figure out all the details of that diagram. What does the Plenum Valve refer to?

So, since I have a diesel that depends on a vacuum pump for the vacuum system that I haven't tested or ever noticed doing anything, I'll assume it doesn't work and will opt to attempt some way to recirc always and keep out the fumes, at least until I can fix the vacuum system and exhaust bolt. I still have two working side windows, a rear sliding window, and vent windows... and rust holes on each door that seem to push cold air in through the inside door handles.

Thanks lots for the detailed explanations and warning!​

 

[chengny]

I've never seen anything besides the hood and brake release knobs by the emergency brake

Yep, you're correct. Trucks equipped with factory AC do not have a manual fresh air damper on the driver's side. Sorry for the bad info.

However, my version does. I have never owned a truck that came from the factory with AC - I have had to convert all of them (3) to AC. And when I do a conversion, one custom feature is that I retain the drivers side kick plate. Non AC trucks have 2 fresh air inlets, the dampers for which are mounted in a opening in the kick plate and controlled by a plastic rod.

When the conversion is done, the RH kick plate gets the recirc valve as designed - to permit MAX AC. But the LH stays a manual vent (factory AC setup has the LH vent blanked off by a full face kick plate). The manual vent normally stays shut. But occasionally it proves useful. It just allows another way to cool off the cab without running the AC or even a fan.


and nothing on the passenger side inside the cab

I bet if you look closely you'll see a curved plastic plate that stands out from the kick plate. It is way up under the dash almost. If you remove that plastic cover you'll see the damper and actuator. Like in the image below:

You must be registered for see images attach

 

[89Suburban]

Use a 6 mil plastic poly film and tape it to the door shell under the door panel to keep the drafts down. Don't cover the cabin vent at the bottom though. That is only designed to flow out, not in. Also under the panel after you poly it you can stick a thin piece of sponge over the window crank shaft to act as a seal to the door panel.

 

[RockyGryphon]

When the conversion is done, the RH kick plate gets the recirc valve as designed - to permit MAX AC. But the LH stays a manual vent (factory AC setup has the LH vent blanked off by a full face kick plate).

So is it possible to install a manual LH vent in an A/C truck without cutting metal?
​

I bet if you look closely you'll see a curved plastic plate that stands out from the kick plate. It is way up under the dash almost. If you remove that plastic cover you'll see the damper and actuator. Like in the image below:

image cut. it's in the previous post.​

I finally saw the recirc mechanism/flap on the truck for the first time and now this diagram makes sense based on that curved plastic piece. So to always get recirc, I should probably disconnect the spring and pod, and prop open the door.
Is it reasonably possible to add a non-A/C manual control and just disconnect the vacuum pod and spring without having to swap the whole thing?

I know it's not likely, but does simply pushing this flap open, close the other flap for outside air?
If not, is the only access for that, removing the whole damn cowl?
I couldn't reach anything through the blower motor hole, but I guess at least it would be an opportunity to clean that area.

Is the outside inlet flap in the cowl the only cab air inlet (aside from my own rust holes, windows, etc.)?
​

Use a 6 mil plastic poly film and tape it to the door shell under the door panel to keep the drafts down. Don't cover the cabin vent at the bottom though. That is only designed to flow out, not in. Also under the panel after you poly it you can stick a thin piece of sponge over the window crank shaft to act as a seal to the door panel.

In my case, the window switches seem pretty air tight (I kind of wish there was a manual crank as a backup when my electric window gets wet/cold and doesn't close), but maybe plastic saran wrap behind the door handle cup/hardware will cut the constant bone-chilling draft on the arm that I assume is being pulled in by the door vent pulling out. Maybe I could put a slider over the vent to manually control flow and close it if I ever fix A/C to keep the cold air at the bottom in the cab.

http://i147.photobucket.com/albums/r316/flamingc10/IMAG1371.jpg ​

Anyway, at least now I've got defrost and won't get blinded and crash! Now if I can only make a recirc work and suffocate on my own bad breath!

 

[chengny]

So is it possible to install a manual LH vent in an A/C truck without cutting metal?

No, only non-AC trucks have that driver's side opening in the cowl. You'd have to make an opening - but it wouldn't have to be pretty, the kickplate covers everything up.

Is it reasonably possible to add a non-A/C manual control and just disconnect the vacuum pod and spring without having to swap the whole thing?

Yes, just strip the diaphragm, bell crank, and springs away and leave the damper (the basic damper is the same on both AC and non AC systems). There should be a silver button on the back edge of the kick plate. Pop that out and run the control rod through the kick plate and connect it to the damper.

I know it's not likely, but does simply pushing this flap open, close the other flap for outside air?

No.

If not, is the only access for that, removing the whole damn cowl?

Yes but removing the cowl isn't hard. Just pull the wiper arms and remove the 3 sheet metal screws that fasten the cowling. The leaf filter under the cowl must come off as well.

But an easier way - to permanently close off the outside air supply - is to cut the hose that goes to the fresh air inlet diaphragm. This flap is normally closed (only opens when vacuum is applied from the controller). The hose penetrates the firewall high in the upper right hand corner. If you do cut the vacuum line to the diaphragm, be sure to plug the hose (on the controller side) so the rest of the system still has vacuum to operate the various dampers.

Is the outside inlet flap in the cowl the only cab air inlet (aside from my own rust holes, windows, etc.)?

Yes. As previously discussed, there is no opening in the driver's side dash cowl as found in non-AC trucks. There are no other intentional openings to outside atmosphere.

 

[RockyGryphon]

But an easier way - to permanently close off the outside air supply - is to cut the hose that goes to the fresh air inlet diaphragm. This flap is normally closed (only opens when vacuum is applied from the controller). The hose penetrates the firewall high in the upper right hand corner. If you do cut the vacuum line to the diaphragm, be sure to plug the hose (on the controller side) so the rest of the system still has vacuum to operate the various dampers.

So if I'm right and my vacuum system is non-functional (old diesel), and there's no residual vacuum in the system, the outside flap will probably be closed and stay that way (I'm assuming it's held normally closed with a spring or gravity) unless something else is going on (debris holding it open), and I can just prop open the cabin recirc flap to avoid outside fumes. Then I can dream about installing dual turbos, a supercharger, nitrous, propane, water, HHO, and burning donuts in 4x4 without choking while I get sucked into a time warp vortex, or driving by the refinery without smelling any stench. Or if the flap is closed and I still get fumes, I have to caulk the firewall and wrap the whole cab in saran wrap.

Thanks for all your expert advice. I think the thread is much improved because of it!

 

[chengny]

That flap is designed in such a way that, even when fully closed, there is always a certain amount of outside air allowed to be drawn in by the HVAC blower and enter the cab.

This feature provides a constant exchange of the atmosphere within the cabin - that is a good thing.

It helps maintain a low level of moisture which greatly increases the efficiency of the defroster system.

It clears the interior atmosphere of unwanted odors and smoke from cigarettes.

But, most importantly, a constant flow through of fresh air ensures that carbon monoxide levels are kept below the point where they are harmful to your health.