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Most of the L-body cars are starting to exhibit a common problem with the heating and air conditioning modes becoming inoperative or stuck in one mode or the other due to the vacuum control harness coming apart at the plastic splice connector. The heat and A/C hand control located inside the passenger compartment and on the left side of the dash is where you adjust the mode, the fan speed and the temperature of the air discharged.

This control unit uses a series of vacuum lines to control the mode and amount of heat that is produced. If these lines become loose or disconnected the system will often get stuck in one mode or maybe the heat wont adjust. It can also cause running problems if the vacuum leak is big enough because the system pulls it's vacuum source from the engine compartment.

The common problem here is that the vacuum harness that is attached to the back of the control head, has a splice connector in it, about 6-8" from where it plugs into the control unit. That splice connector, over the years, falls to pieces and the lines become disconnected. It is difficult at best to try to guess which lines go to where when this happens. So below is a picture of the connector in good shape and showing the location of the different colored lines. I have discovered this arrangement works on 85, 86 and 87 L-body cars that are A/C equipped from the factory. It may be different for non-AC cars.

To repair this, simply use short pieces of small diameter silicone hose or windshield washer hose and something like a zip-tie on the ends to hold them snugly in place, and splice the lines back together as shown in the pictures below.
 

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5,344 Posts
yep my turismos just crumbled to pieces like a dirt clob, had to redo the lines with a connector with vac hoses from a 98 dodge ram assembly
 

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I might even throw a pic of the dodge ram vac harness for future reference
 

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THIS is the info I've been looking for! Long story short:

1. Started diagnosing A/C. Figured it could be a bad compressor so replaced that and h-valve/accumulator/etc.
2. Compressor clutch still won't engage, even after jumping connections, figure it might be "interface-side"
3. Start taking apart left-side dash panel to check for lost connections
4. Start getting high idle (1800-2400)

I probably broke the connector when I was pulling on stuff which started causing all these problems.
 

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1987 GLHS 0564
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794 Posts
I just experienced this connector failure as so many before me have.

Thank you OP for posting the photos of the lines still connected as mine were just lose under the dash since the connecter was completely gone. I was wondering how the heck I am I going to t be able to trace them out for proper operation and saw this swing post.

I used 7/64 vacuum line to splice the line inplace of the connector and it worked like a champ. I also printed up the photos and placed in my cars file for possible future reference.
 

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1989 Dodge Shadow 2.5 non turbo 3 speed automatic
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340 Posts
I guess I’m lucky on my shadow the lines are still soft and bendy and the junction brick is still a stiff but rubbery material. The reason I know is the foot/face door broke and would only supply foot air. It ended up being because the thin plastic piece that holds the 2 door parts to the shaft had snapped of and was letting the front door stay sealed to the face duct hole. I tried epoxying a half washer onto the front door but it broke fo after it was all back together in the car.🤦🏻 I ended up drilling two holes through the top and bottom of both doors and sowing it together with fishing line. And the whole time I could see what I was doing.
 

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