So I stopped looking at this because I just got tired of being up underneath the dash etc.

Could someone tell me if the blend door actuator is faulty could that be my prob?

No matter what setting I put the controls on, air trickles out the dash vents. From what I can tell the doors in the center stack are good.

I can't get concentrated air out of a selected setting which makes weak air flow everywhere.

This truck is after growing on me and I'd like to take another stab at this before winter hits.

Cheers

 

I'm guessing the hose is pulled off the vacuum reserve tank in the inside rear inside of the driver's side front fender. Starting at the intake, hose goes up and over the brake booster, then down to a tee where line branches off and goes through the firewall - ending up at the tank inside the inner fender (difficult to see). Sometimes the port gets broken, but hose mostly gets pulled off.

If not check for vacuum system inside the vehicle to not be leaking. This is done with a hand vacuum pump/gauge on the hose going through the firewall.

Good luck

 

So I replaced the blend door actuator, seems like the factory unit was a better design, and I even bought the AC delco replacement. (new one is GM# 89018365 vs the factory 16163982 It is the one for the auto climate based on the pin count, but the cylinder that grabs the axle end is just plastic and not metal with ribs like the original. I've since confirmed the part number too. Doesn't seem to grip the axle well, but the door is slowly turning in stages (I opened up the "to service, cut here" port and watched the door)

There's a horde of gremlins in that dash. I have vacuum at the driver side fender actuator like you mentioned, and the hose was secure when I checked it.

I buttoned everything up, pulled the rdo fuse for a few minutes. Put it back in and started the truck. HVAC didn't seem to cycle through anything like it should have.

Now I noticed I have no vacuum at the actuator that is immediately before the blend door actuator - the connector is good. No hiss or movement no matter what I put the setting on. I haven't opened the dash bezel in quite some time so this is not something I knocked loose in doing this replacement.

Wonder if the main HVAC vacuum module is at fault...

How can I get the truck to properly reset the HVAC settings with the RDO fuse?

 

It appears all my doors are still intact. I even used my newly acquired endoscope camera and shoved it in through the vents and everything from what I can see looks good. (no debris)

I'm concerned the new BDA is not gripping the plastic stud well enough, or maybe the stud is rounded somewhat making it harder to grip.

 

I am not "seeing" how a blend door problem reduces air flow or air volume. The blend door simply directs the air flow either through the heater core or the evaporator.

Now if temp is the issue then yes blend door.

There is a HVAC diagram; have you seen it?

The vacuum actuator behind the glove box selects fresh air or recirculatred air. There will only be vacuum there when the non-default position is selected. (not sure which is default: fresh or recir).

The two vacuum actuator just to the right of the accelerator pedal controls air direction: dash, floor, defrost.

The HVAC controller in the dash receives engine vacuum via the black hose and directs it to the actuators as needed.

Hope all of this helps.

 

Actually, you've been a great help and I appreciate your attention.

I was thinking that if a blend door was only opening part-way it would restrict flow.

My floor vac module I replaced already, even though the original worked. I had the brand new AC part and installed it anyways. It's almost like not everything is getting full vacuum requirements to operate.

I have vacuum at the main black line that comes through the firewall. I can hear the 'hiss' when I disconnect the harness at the HVAC module where all the vac lines meet that's in behind the hvac controls.



I have 2 vac actuators behind the glove box, one that opens the recirc door and it does it flawlessly without any issue at all. Then there's another that I had to remove to change out the BDA, this one from what I can tell is not getting vacuum and I'm not sure what selection it has to be on (not sure what that door is called) When I unplug the vacuum line to it, there's no vacuum whatsoever.

I had a video here somewhere that I'm trying to find it had module ever worked that is behind the dash (not the recirc one)

 

If you have this diagram and if it shows what the vacuum should be at what points, please post it. I might end up getting a mityvac yet.

 

I took out the battery and the battery tray tonight. The vacuum actuator there is intact and has the hoses connected properly, nothing loose.

If I squeeze this actuator I can hear air come out of the fitting that is directly center of the back of the engine bay with 2 vac hoses and an electrical harness attached (this is mounted up above the spider on almost to the windshield cowl). If I place my finger over the small hole on top of this unit the hiss stops. Must be an internal release valve or something?

Not sure if that's normal, but that unit looks otherwise intact.

 

Been following your posts for a while and had suggested to check for a broken blend door a while back. I have since fixed mine and have warm air to the floor again.
What caught my eye was that you have gone to the actuator (under the battery) to engage the front differential for 4x4 operation. The switch with the vac hoses relieves pressure in the actuator so the differential will dissengage. If the hoses are reversed vacuum wont vent and the differential may not disengage.

 

Have not been able to post the HVAC diagram.


The vacuum switch on the firewall is to engage the right front axle when 4wd is selected. Should have vacuum on the hose that does not go to the actuator under the battery tray.

Are you sure the blower motor is turning at full speed?
Are you getting air flow out of....say floor when you have defrost selected? If one of the actuator has failed such that air flow is going to two places instead of one, this would seem like reduced air flow.

Other thoughts that would reduce air flow:

If the heater core or evap coils are covered in dirt.
If the blower motor resistors are burnt or failed in some way,
If the fan is not fully attached to the blower motor,
Mouse, squirrel, etc..... nest in air distribution ducting,
Blower motor not getting full power due to burnt or damaged wiring.

I know that fan settings 1 & 2 are pretty much useless in my Blazer regarding air flow. I have thought about changing the resistors for these settings, and I would if I could do this without cutting into the air ducting.