Does anyone happen to know exactly where the vacuum line that goes to the HVAC control enters into the cabin from the engine bay? I went looking and have not been able to locate it; appreciate any hints.

 

In my '99 it enters the fire wall on the drivers side a few inches inboard of the interior fender apron and about 6 to 8 inches below the top of the firewall. It is part of about a 1" diameter bundle wires.

 

I know I found a vacuum line that disappeared into a wiring bundle so I guess I did find it. Odd though, as I thought I remember seeing a vacuum line by itself attach to the firewall and I had been looking for it....perhaps I am remembering a different vehicle.

Thank you Christine_208. I was hoping I could disconnect and cap-off the HVAC vacuum line and then pull a vacuum on the HVAC vacuum system to see if there was a leak...so I did not have to pull the HVAC control out of the dash....looks like I will be taking the dash apart.

Did you get your 4wd working?

 

LannyL81,

You should be able to disconnect the HVAC vacuum line from the Tee in the vacuum supply line and put a vacuum on it. I know this as I've done exactly the same test with my Mityvac tool.

My replacement vacuum lines seemed to not exactly fit so I used zip-ties as mini-hose clamps to secure them.

As for my 4wd, mine never stopped working but thanks for asking.

 

The vacuum line you remember seeing separately could be the rear washer line. They kept that away from the electrics.

 

Christine, I was not sure that the vacuum line that I found and you described was just for the HVAC.....so very good to know and yes I will do exactly the same test as you did.

I am trying to determine why I have some heat coming out of the floor vents when I have the HVAC controls to OFF and the temp control fully cold. I pulled the temp door actuator and checked its operation, it was 100%....one click of the control, one step of the motor. Thought I had found the problem when I noticed that the ground wire terminal in the actuator connector had been pushed back a bit so maybe was not making full electrical contact. Fixed that but no change.....so figure something must be leaking and that is what has lead me to the HVAC control vacuum.

Something I should have done when I had the temp door actuator out was to drive around and see if the motor was moving even though the controls were not moved.....hmmmm....may have to go back and do that if I find no vacuum leak.''

Rusty Nuts:...yeah that could be it.....I have yet to find what I am remembering.....but that is nothing new.....blasted CRS!

Thanks to both of you.

 

Have you checked the blend door actuator? It electronically controls the temperature but maybe its function is coordinated with the vacuum actuated parts.

I think I asked this before but... Are your vacuum system hoses in the engine compartment all correctly connected? (Somewhere on this forum you should find a proper diagram.) You might try bypassing the vacuum storage tank and 4wd actuator line to see if the engine at idle (with the greatest vacuum) will run the HVAC. There is also the one-way vacuum valve that must be installed in the right direction.

If all that is good it might be the HVAC vacuum solenoid that lives inside behind the ash-tray that is bad. I suspect mine is going bad as I've checked all of my vacuum lines but when under hard acceleration (i.e. little engine vacuum) the air flow will direct from defrost to the vents. Otherwise it works fine.

If it weren't such a hassle to get behind the dash, I would have had all of my HVAC issues worked out a long time ago! LOL

 

I did check the blend door actuator or temp door actuator as I called it. Operation was fine. Vacuum hoses are fine, all in the correct place, replaced them all about three years ago.
I did not spend any time with Blazer today so will have to do some troubleshooting another day.