HVAC selector vacuum leak

[88mjblue]

Renix 4.0, no AC, no cruise control.

 

My HVAC system only blows out of the windshield defrost vent. After researching and finding that this is a common issue caused by a vacuum leak, I traced my vacuum lines to find the leak. I followed the main vacuum line that comes out of the intake manifold and goes to the vacuum canister in the passenger front bumper. The line was intact and attached to the bulb in the bumper.

Then I went to the back of the controller in the cab behind the dash faceplate and checked that the lines were plugged in. (they were)

Tracing those 4 lines from the dash, I now find this blue vacuum line (picture below). It is not plugged in to anything!

I think this is the problem, but I don't see any lines where it can be re-attached...

Can anybody confirm that this blue line is for the HVAC vent selector, and can anybody confirm what the other colors are?

I think the green and yellow lines are the vacuum lines to engage the front axle.

 

[Stacks]

That blue line isn't supposed to be plugged into anything. It is a 'vent/breather' line for the transfer case vacuum lines.  Red is the vacuum source for the tcase to switch, green and yellow work the disco and the white one goes to a vacuum switch that turns the 4x4 light on in the dash.  :)

[88mjblue]

That blue line isn't supposed to be plugged into anything. It is a 'vent/breather' line for the transfer case vacuum lines.  Red is the vacuum source for the tcase to switch, green and yellow work the disco and the white one goes to a vacuum switch that turns the 4x4 light on in the dash.  :)

 

So none of these vacuum lines are related to the HVAC system??? I thought I saw the same colors coming out of the the selector... 

[Stacks]

Nope.  There is a black line that comes from the vacuum canister and is the vacuum source going into the inside controls.  There is a white line that comes out very close to the black one and the white one goes to the heater vacuum control.   The thing on the end of the blue line is a one way valve.  If you follow those colored lines shown in your photo, one direction goes to the tcase and the other ends up at the axle disco.  The colors are a coincidence. 

[Bobolink]

Take it from me, the leaks are sometimes elusive, especially if you only LOOK. I once tore into my dashboard, just knowing for sure that I had no holes anywhere under the hood, having checked three or four times. But after finding nothing under the dash, I put that back together and once again looked under the hood. Finally found one small hole in the black plastic line, rough to the TOUCH, under the pressure bottle tray three inches or so before going into the firewall. By touch was the only way I found it.

[88mjblue]

Take it from me, the leaks are sometimes elusive, especially if you only LOOK. I once tore into my dashboard, just knowing for sure that I had no holes anywhere under the hood, having checked three or four times. But after finding nothing under the dash, I put that back together and once again looked under the hood. Finally found one small hole in the black plastic line, rough to the TOUCH, under the pressure bottle tray three inches or so before going into the firewall. By touch was the only way I found it.

 

Bobolink, I think you may be right.

I just did what you describe, I began to tear my dash apart and everything seems to be connected back there.

I will go through with the carburetor cleaner to find the leak which could have eluded me under the hood.

 

Just to confirm, the black line we are talking about is the smaller black line that goes from through the firewall (exits next to the heater control valve line) and then parallel with the main vacuum line that goes to the canister in the passenger front bumper?

[88mjblue]

Nope.  There is a black line that comes from the vacuum canister and is the vacuum source going into the inside controls.  There is a white line that comes out very close to the black one and the white one goes to the heater vacuum control.   The thing on the end of the blue line is a one way valve.  If you follow those colored lines shown in your photo, one direction goes to the tcase and the other ends up at the axle disco.  The colors are a coincidence. 

 

Yep colors are a coincidence. These colored cables are actually electrical, not vacuum lines that connect to the inside controls.

I checked back there behind the dash faceplate and everything was connected.

 

This image explains it, for those who are wondering:

 

And here is my own image from back there:

 

 

I didn't take the whole dash out, but just checked to see if it was plugged in (and it was)

Now I will try the carburator cleaner method, and hopefully, as Bobolink has suggested, it will turn up somewhere...

[88mjblue]

Take it from me, the leaks are sometimes elusive, especially if you only LOOK. I once tore into my dashboard, just knowing for sure that I had no holes anywhere under the hood, having checked three or four times. But after finding nothing under the dash, I put that back together and once again looked under the hood. Finally found one small hole in the black plastic line, rough to the TOUCH, under the pressure bottle tray three inches or so before going into the firewall. By touch was the only way I found it.

 

Well, you were right, Bobolink. I traced the whole line again, and found a small hole in the exact spot you described! It was worn down from rubbing against the crimped hose connection that goes to the pressure bottle. 

 

 

I taped it up with some duct tape to see if that would solve the issue (and that there were no other small holes anywhere else) and it worked!

I know that is not the best way, how do you fix holes? Cut and splice together with something? Glue? What have you guys done in the past to repair a vacuum line without taking the whole thing out and putting in a replacement?

[Bobolink]

Yep, find a regular small piece of vacuum hose about 3/32" I.D., or so. Cut the plastic tube and splice together with the vacuum hose. Not exactly sure of the ID of the hose I used to do the splice, but of course just be sure it fits tight on the plastic line. Should be a permanent fix.

[Dillithium]

This thread has given me new hope to repair my vacuum leak, I'll be tackling this first thing tomorrow.

[ParadiseMJ]

Other areas for vacuum leak on that black line is under the battery tray.  Acid corrosion etc.  I prefer replacing the entire line instead of patching it up.  If the line is old, chances are there are other potential leaks down the line.  The bulk vacuum line is cheap.

[88mjblue]

This thread has given me new hope to repair my vacuum leak, I'll be tackling this first thing tomorrow.

 

Definitely go for it, and don't give up! I thought I was never going to find that leak and would have to take my whole dash apart as someone had mentioned. But I went back a third and fourth time to really search and I felt along the whole vacuum line from firewall to canister with my fingers around all sides and finally found that tiny hole, plugged it up and boom! I've got warm toasty heat coming out of the vents, floor thingy, and anywhere I want it.

[Knucklehead97]

Sorry to bring this back up. But which color vacuum lines do I need to cap off for the CAD elimination? Do I need to cap off the one to the Tcase (red) or just the ones to the CAD?(green and yellow)

[cruiser54]

Sorry to bring this back up. But which color vacuum lines do I need to cap off for the CAD elimination? Do I need to cap off the one to the Tcase (red) or just the ones to the CAD?(green and yellow)

I just pull the whole harness out. 

[Knucklehead97]

 

 

Sorry to bring this back up. But which color vacuum lines do I need to cap off for the CAD elimination? Do I need to cap off the one to the Tcase (red) or just the ones to the CAD?(green and yellow)

I just pull the whole harness out.

I planned to take out the metal lines that lead down to the CAD. I just didn't want to cap anything that worked something important. If you pull the whole harness out then what do you cap? i want to get rid of as many useless components as possible to clear up engine compartment space.

[Dillithium]

Righto, I have a follow up question.

 

I've followed the line as pictured below:

 

 

 

 

As you can see, this small black line runs towards the coil pack and seems to be lodged between part of the motor mount bracket and the fenderwell. I'm 99% sure this is not the way it's supposed to go, but that little connector thing I'm pointing at has me on the fence

 

After it passed through the motor mount bracket, it loops back towards the battery.

 

Secondly, there's this thicker hose coming out of the firewall:

 

 

This hose leads all the way to the vacuum canister in the front, but is just dangling there without any connection. It's coming from the firewall, I can't imagine it's a breather hose. Does anyone know what that is?

[88mjblue]

That thicker hose should connect back at the intake manifold as shown below. It routes from the vacuum canister in the passenger front bumper and makes its way to the firewall, goes behind the engine along the firewall and then attaches to the intake manifold. This is a major vacuum line that also supplies vacuum for the front axle disconnect.

As for the smaller diameter hard plastic black line, you're correct – that should not be going through the motor mount, it should come out of the firewall next to the pink heater control valve line, and then head over to the passenger side wall joining up with the larger line that leads to the canister in the front bumper.