Dual AC system question

[Bill Schmidt]

A few months ago, I bought a 1998 3500 extended van with front and rear factory AC. It has 108k and drive train pulls like new (transmission was rebuilt about 3k before I bought it). Front blower motor was not working, so I had it replaced by reputable AC shop. AC seemed to work normally, but no real hot weather to really check it out until recently.

The problem I've noticed, is the rear AC blows cold air, but the front is not nearly as cold. I get a good sized condensation puddle under both units, and front evaporator is nice and cold; but that cold air is somehow being partially warmed before it enters the cabin. Compressor is running normally, so I think refrigerant charge is good. Any ideas on what's going on?

[dizzyD]

Not exactly sure, but their is a blend door that diverts the heatercore and a/c core into the duct works, This door may not be closing (or opening) correctly. Can be caused from mis alignment of selector, something stuck in door path, or...

[alloro]

Pull out the glove box interior and you'll find the blend door motor and linkage behind it. Like dizzyD said, it could be as simple as the blend door not swinging all the way over and some heated air is sneaking through and mixing with the cold air.

[stev]

You might not find the bleed door where Alloro had mentioned unless the unit was a pre 1998. You might find the bleed door vacuum actuator on the passenger side of the vehicle under the hood. It usually sits right behind the headlamp. that controls the linkage that moves the vent bleed door. My 1999 B1500 had this door stuck in blend mode. So the AC and heater were so-so at best. Not sure why this door get jammed on these vans.

[alloro]

You might find the blend door vacuum actuator on the passenger side of the vehicle under the hood.

That vacuum actuator is the fresh air vent that closes when you switch to MAX A/C. The blend door motor (which is electric, not vacuum) for a 98 is right where I said it is, behind the glove box.

[Bill Schmidt]

I'll be checking it out soon.

[dizzyD]

Keep everyone posted of your findings

[RamVanMan]

I also noticed inconsistent AC operation. Not with the rear AC (which isn't operating now, period), but with the fact that on AC MAX - outside air shut off - it was less cool by far than Normal AC.

Discovered the vacuum hose - small grey in color, which pokes out of the firewall in a molded rubber grommet with 3 other hoses, was broken & cracked from heat. We used a next size larger hose to go over it & reconnect to the remaining good end, over to the vacuum cannister behind the PS headlight (as mentioned above).

Problem solved. Hope this helps someone !

David B.

[donnie71281]

Where is the blend door in a 96? Am i correct in thinking that pretty much the whole dash gets torn out for this? Or can it be adjusted at the back of the controls.

[97B2500CCV]

On the 97 and earlier it is under the hood next to the fire wall on the passenger side. Have some one slide the hot/cold selector switch and with a flashlight (if needed) look up towards the top and you will see a cable sliding back and forth. On my van I found that it needed a small adjustment to get the internal air nice and cold. With out side temps in the mid 90's my AC will get down to 38 coming right out the vents.:D

97 and earlier has manual slide blend door control.
98 and newer have an electric controlled blend door.

[donnie71281]

exactly how did you make adjustments to it? I assumed it was a cable that was more or less fixed and couldn't be adjusted. How difficult is this to do and what was your process/how did you know wen it was adjusted right. . . extremely curious!!

[donnie71281]

exactly how did you make adjustments to it? I assumed it was a cable that was more or less fixed and couldn't be adjusted. How difficult is this to do and what was your process/how did you know wen it was adjusted right. . . extremely curious!!

[97B2500CCV]

After determining which way was for the cold side I found that there was a little more that the door could go and I would have to look but I did find that I could slide the cable connector on the rod that it controls. It had been a year ago that I did this. I won't have time tomorrow to look at it but I may Saturday. And I will see if I can take some pics also. I do remember that it took less than a minute to make the adjustment.

[donnie71281]

That would be great. I will investigate tomorrow after i get off work. And then see if/what you get back to me with and then i'll tear into it. Being that i rebuild one of a kind pianos for a living. . . figuring things out is my forte. . .

[stev]

According to the FMVSS (Federal Motor Vehicle Safety Standards) requirements, the outside fresh air vent needs a minimum 10% bleed into the vehicle. Why? because the build up of carbon dioxide from breathing will put people asleep behind the wheel for an accident.

So, whatever you do, just realize the total outcome of this. ;)

[donnie71281]

I was mainly curious in case i ever have a problem with the blend door. Though i see, on here, there are more issues with the electric motors than the manual.

As wrong as it is. . . i couldn't stop myself from laughing at the falling asleep thing.

I won't hold my breath on any 96, or new van, being that air tight. . .

[97B2500CCV]

The temperature blend door is only for how hot or cold you want the air to be. That is what is by the firewall on the 97 and earlier vans and as Alloro said is behind the glove box on the 98 and latter vans. These is controlled by sliding or turning the knob which says
Cold-------------Hot.

The Recirculating/Fresh Air blend door which is behind the passenger headlamp is for recirculating the interior air on those really hot summer days. It only closes when the AC is put in the "Max" position. Normal AC, Bi-level, vent, Heater Defrost all use only fresh air. Even with the door fully closed by the vacuum motor there will still be some fresh air coming in.

[alloro]

Even with the door fully closed by the vacuum motor there will still be some fresh air coming in.

The leakage is 10% by federal standards. I guess they don't want anyone falling asleep while driving. :)

[donnie71281]

So is the 10% achieved by the actual blend door not closing all the way on each setting or through construction of the door and whatever else? Is the 10% percent divded up between the two max settings(all the way to cold or hot) or what? This is a surprise to me. . .

[dizzyD]

The 10% is a manadtory "rule" All systems do this, even to some extents, new housing systems. Industrial section has had this in place for some 30years.
As for the auto's, typically their is a fresh air "trap" in the cowl section behind the hood, where the wipers are at. this allows the fresh air in and their are "wanna-be" one-way flaps in the back of cab to let air out. there is a door that closes on recirulate mode that closes, but either a knockout or section is removed for the equivalent 10% fresh air

[alloro]

Is the 10% percent divided up between the two max settings(all the way to cold or hot) or what?

We're talking about the fresh air/recirculate door, not the hot/cold blend door.

[97B2500CCV]

These are two separate doors with two separate functions. The Recirculating/Fresh Air Door only controls whether the air to be conditioned is all fresh air or when the AC Max is selected recirculating the air from inside the cabin by the passenger side foot well.

After the air intake is chosen then the air goes through the AC Evaporator Core to cool the air, at this point the Temperature Blend Door says whether to bypass the heater core of allow some or all of the air to go through the heater core, depending on where you put the temp selector at.

[donnie71281]

That was going to be my next question. I thought a leaking blend door would kinda defeat the purpose. Which is why i kept questioning it. I guess i'll have to re-read part of this thread and see if i missed someone saying recirculate or blend door. I've been known to not see things right infront of me. .

[97B2500CCV]

Here is a diagram of the HVAC component layout. As you can see the Fresh/Recirculating Door. This door stay on fresh air (outside air) unless you select AC Max then it closes (90%) to bring in the air from inside the van which helps to cool the air faster on hot days is just to the left of the fan motor. Then the air goes through the fan up to the AC core and here is where the temperature selector tells the Tempature blend door how to adjust the amount of air that is allowed to go through the heater core.

http://i734.photobucket.com/albums/ww346/MobileAutoRepair/97earlierHeaterAC.jpg

[donnie71281]

Very nice diagram. This is how i originally thought it was set up, but at some point let myself get confused. Is this from a service manual? I'd like to get one. Any suggestions? I've used the a Chiltons for my old grand prix, but i have to say i don't think it was all that great. . .

[97B2500CCV]

I bought my service manual from off e-bay. Type in your year, make and model. There is nothing like the factory service manual. I have the Haynes and it is poor compared to the OEM one.

[alloro]

select AC Max then it closes (90%) to bring in the air from inside the van which helps to cool the air faster on hot days

This has always irritated me. Why do they only design a MAX A/C and not a MAX HEAT? There are some cold winter days where pulling 10% outside air and 90% inside air through the heater core would sure help warm up all of that space we have.

[donnie71281]

I agree completely.

I remember when i went to college my mother had me take her 82 Vandura 250. Small 305 4 barrel carb too. . . barely moved that thing.

Anyways, it did not have the dual system and only had the front. It NEVER got even a little cooled down in the summer so i used the windows all the time. In the winter. . . you were better off taking a blanket. Northern Ohio is a Bi@#h in winter. Not that going to school in wheeling was much better.

I can remember her hanging up a blanket to help make it warm. Nothing looks better than that. . .

Maybe the industry uses the following saying:

"you can always put more clothes on but can't take a whole lot off"

who knows. . .

[97B2500CCV]

Not sure if this would help but might take the van and let it heat up some to the point where good warm air is coming out of the vents then put it on AC Max but slide the temp control all the way to the hot side. 1) it will recirculate the air, and 2) with the compressor running it will help dry out the interior and windows faster.

[donnie71281]

I inherited the van when my mother passed away this june so I've not experienced a winter in this Van. I'm sure it will be better with the dual system, unlike that old GMC, so i will definitely try that. Never would have crossed my mind. . .