i really haven't seen that prob. b4, did you check the vac ball that hangs down from the hood driver side? And the plug in at the manifold?

 

I didn't check at the manifold but I checked all the way down the line from there. Before the T, and on both other T connections. And got the same vacuum from the gray vacuum tube on the HVAC vacuum module. At idle, I got about 15 hcg per my gauge.

 

My ac will only come out of Defrost vent and floor vents. I have checked the vacumme underneath the hood and it is giving out pressure, also checked the connection on the back of control in the dash and also getting pressure. However when I turn to max ac it will only pump ac through the defrost vent and floor vent. While driving it will sometimes kick on through middle vents but not very strong. Could someone please help me out.

 

I am having the EXACT same problem today.. AC blowing thru the defrost and barely through the face vents. I found that my vacuum hose nipple had broken off my vac. reservoir, under the hood of my '96 blazer. When my son held his finger over the open hose end, the vents inside worked fine.

Now i have to figure out why i cant charge the AC beyond 45psi pressure, even though i have put two cans in it.

And why do the cans cost $12 each now? Didnt they cost about a buck when they first came out???

 

I am going to try and change all vaccume hoses, as most of mine look pretty bad just from dry rot. I hope this will work, just seems crazy that the vaccume is working very well but a simple thing like replacing the hoses might solve this problem. Will update when done.

 

It would be great if someone could tell us what the vacuum is supposed to be / what is normal. I have the same (15 hcg) all the way down the line but I have no idea if that is too low or not.

 

So the vac on mine has only one T, i noticed lastnite though, when i really get down on the gas the vac loses pressure then goes to floor vents and when you shut the suv off it blow to the floor aswell only when the engine is on dose it blows right.

 

I *think* have this fixed for now. Based on the above, I did the following:

1. Disconnected the vacuum hose that T's off the HVAC one and goes over to the 4WD actuator and capped the T connector. Figure I'll address one issue at a time.

2. Replaced the vacuum hoses from the valve cover to the check valve, the check valve to the vacuum ball, and the check valve to the hose that goes through the firewall.

3. Replaced the check valve itself.

4. While I was at it I replaced the PCV valve (and managed to break the elbow and the cab that connects to the valve cover with the vacuum connectors on it but that is another story.

6. Replaced the HVAC vacuum controle valve that is inside the HVAC control head.

As of now, everything is working right ... but that is sitting in the garage. We'll see how it does on the first few trips out. Of course, I still need to track down the 4WD issue. I wonder if there is a leak somewhere down that line that was at least partially causing this.

One other thing I learned along the way:

"Normal" vacuum at idle is 17 to 22 inches, AT SEA LEVEL. I am at 4500' and you are supposed to subtract an inch for each 1000'. So my 15 inches is completely normal.