I know this has been discussed several times. Now that i have my blower fuse problem fixed im only getting air out of the defrost ducts. I downloaded the vacuum diagram that Christine posted. Under the hood everything is just as the diagram shows. I am thinking this is going to be in the dash.

 

When I was researching this, I learned that the hoses in the engine compartment can pass a visual inspection but can still leak or have a bad seal at a junction. The only way to be sure is to do a vacuum test. A Mityvac hand vacuum pump is super useful for locating the hose(s) that are leaking, either in the engine compartment or under the dash. If you don't have one, you might be able to get a loaner from Autozone or another auto-parts store. This helped me figure it all out.

 

Thanks Christine
thats the plan for tomorrow. Up and at it early.

 

My truck's t case switch leaked and allowed ATF into the system.. the 4WD actuator, reservoir, and into the dash.. The actuator that moves the face vents in the center was the nastiest of the 3, but as far as I could tell, each actuator still held vacuum.

I also flushed the colored under dash lines with de greaser.. I think that's what fixed it honesty, but I went ahead and replaced all 3 actuators anyways. It was very depressing putting it back together without being certain the issue was fixed.

If you can't find new and assuming yours is a 4x4, look for a 2WD at a junkyard.. It won't have the leaky t case switch!

 

I am wondering how you get to these actuators. Ive gotten everything out, radio, front glove box, all the covers under the dash. I can just see the one thats on the passenger side. Also i see where the small black vacuum line goes from the drivers side under the hood but thats where i lose it. All the colored lines coming off the module all go to the passenger side of the truck. Also when i took the tee apart under the hood i did notice it appeared to be wet.

 

 

The black vacuum line that supplies the HVAC from the engine compartment is hard to find in the rats nest that is under the dash. However, it is what supplies the HVAC control module/switch. I have the Automatic Climate Control (set the temperature) type but most are the ones that control the fan speed manually. Either way it is possible for it to leak.

 

I took all the lines off the module and the only one that had vacuum was the grey hose. Does this make sense to anyone. I thought it qas supposed to be the brown one. Think im over my head with this one. And i went to Orielys and AutoZone to see if i could get a check valve for the HVAC. They had no idea what i was talking about.

 

The grey/ black hose is the vacuum source if I am not mistaken. Runs from the driver side firewall under the dash to the passenger side.

That said, it makes sense that if you'd disconnect everything that it'd be the only one with vacuum.

Here's the check valve p/n. ACDELCO 1550568
I'd also replace the vacuum reservoir.

 

Got the reservoir on order. It will be here today after 3 but ill be at work so the only chance i have will be acter 3 sunday so i will do that. I will stop by NAPA and order the check valve today. Thanks for the information. Any help here is always appericiated. Also are you saying the black hose going through the firewall turns into the grey hose under the dash. If that is the case, then i have pleanty of vacuum to the sele tor module. If so then it has been narrowed down from the selector switch out to the blend. Time to purchase a mighy vac.

Rick