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Discussion Starter #1
Well when I put my lift on, I accidentally broke the lines going down to axle. The cad vacuum lines that is. Well to make a long story short, you cant just buy the flex part of the lines going down to front axle, you have to buy everything back to the t-case. So the mechanic at the local dealership told me to just get some regular vacuum tubing and make my own, thats what he does, plus I could make it any length I wanted given the lift. So I make my own and all is good. Then I'm going down the road and now the heater keeps defaulting to defrost off and on. WHen I'm riding down the road and it defaults to the defrost, if I let my foot up off the gas it will come back to where its supposed to be. This means I have a vacuum leak somewhere. I checked my homade lines and they are all good, I'm thinking its a just a coincidence that it happened at the same time. Anyways, been over the complete truck and cant find anything off or missing. Has anybody had this vacuum leak trouble before? Is there somewhere on these trucks that the lines like to come off or crack?
 

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there is a box under the cowel area between the hood and windshield that holds a vacuum to keep the air blowing out the proper vent. they crack all the time and loose vacuum. check that out, and just fiberglass or silicone it if you find a crack. dodge's answer was a little check valve you add in line from on the vacuum hose running from the intake to the box. did you replace all of the vacuum tubing running to the axle? I think the tubing might have also had a valve in it and if you are just running straight rubber hose now, you might be losing vacuum that way
 

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Man, thats a mystery to me. Why would your vacuum lines that activate the 4x4 hubs be affecting the heater and defrost actuators? I'm not sure, sounds like you have a different problem under the hood somewhere. I had a vacuum leak on those same lines and it caused the 4x4 to inactive. Replaced the lines and wah-la!! I can get back into 4x4. Never had any issues with the heater or defrost. :-?: :dunno:
 

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Did you check the lines at the manifold? Should be one line coming off the PS that then splits and goes to the cruise control. the line continues to a check valve, and then splits agian to the HVAC controls, and one line going behind the manifold down to the Tcase that is light green to yellow in color. Simplist vacume system I've seen on a late model vehicle. Carefull with the Tcase line, as it will break just by looking at it.
 

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Discussion Starter #5
I didnt think was a check valve in the line to the axle. All I replaced was the two flex lines that run from the frame down to the front axle. I replaced from the steel lines on the frame, and did away with that little rubber block on the axle and just hooked the tubing straight up to the two ports. Yes, I made sure I hooked the right line to the right port. I triple checked to make sure everything was good. Where's this box under the cowl your talking about? In the cab or outside the cab?
 

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you'll have to remove the wiper arms and the cowl cover to access that vaccuum box....

Rick
 

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there is a tsb on it somewhere. check this site http://dodgeram.info/tsb/index.html
 

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here is the tsb http://www.dodgeram.info/tsb/1996/24-01-96a.htm
 

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No the check valve is up by the intake.

A leak in the 4x4 systems vacume will affect everything. Been there, done that.

You could get one of those rubber cap a$$ortments, then pull off the vacume line that runs down to the Tcase, and plug the port by the manifold. If the leak is still there, then you know it's not your 4x4 system that is causing the problem. Basicly it's a process of elimination.

One other method to find vacume leaks is to take a propane torch, or oxygen with no flame, just the gas and run it over the lines. Any change in idle will show you where the leak is. Works great with ole carbed motors, not sure about and EFI motor though.
 

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This buliten is for the 94-96. My 97 has it. this was the one that was causing problems with not a lot of heat aat 45 and above mph. I just picked up two today to replace my intake one and the ac/heat controls. I have heat now and it doesn't switch back and forth to defrost.
 

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Discussion Starter #11
what bulletin?
 

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Discussion Starter #13
I did Lee. I just thought he was referring to another bulletin of his own that he had found somewhere else but forgot to link.
 

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Man, thats a mystery to me. Why would your vacuum lines that activate the 4x4 hubs be affecting the heater and defrost actuators? I'm not sure, sounds like you have a different problem under the hood somewhere. I had a vacuum leak on those same lines and it caused the 4x4 to inactive. Replaced the lines and wah-la!! I can get back into 4x4. Never had any issues with the heater or defrost. :-?: :dunno:
The answer to your question is that the lines meet at a T under the hood near the firewall. Dodge decided to run 1 vacuum reservoir to power every vacuum powered accessory in the truck, so basically at some point or another in the truck vaccuum system, every line will meet and branch off. Sometimes directly off an inline check valve, or sometimes indirectly, like CAD to t-case, t-case to tranny, tranny to actuator, actuator to reservoir. So its all one system in a general matter of speaking. When he installed his custom lines, it increased vaccum pressure from CAD to T-Case, but the extra pressure caused it to suck air through the next biggest hole in the system down the line. I.E, the next biggest leak which probably went from vent actuator to check valve to reservoir. I hope this answers your question thoroughly
 
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