1998 Dodge Ram Cummins 5.9, lost vacuum behind fire wall.

[Jnuehring]

Need some help, Vacumn line from firewall into HVAC where does it end on the HVAC side. I have inspected and repaired the engine compartment still no vacumn to hvac system. have dash dissembled I can view the multi colored vacumn lines, the connector that they run to and through up to the HVAC control, but no line from engine compartment.

 

[BigPapa]

Check this YouTube video. I haven’t watched the whole thing. Hope there’s no bad language.

 

[Jnuehring]

Check this YouTube video. I haven’t watched the whole thing. Hope there’s no bad language.

has nothing to do with my issue. thanks

 

[BigPapa]

The video describes the routing of the various vacuum lines. The title of your post said you lost the vacuum to the HVAC Controls and wanted to know where it is.

The black line behind the turbo goes through the firewall to the vacuum connector where the multicolored tubes, the vacuum harness, run to the control panel. They then go to the actuators. The “Vacuum Reservoir” is a carryover from gas trucks. The diesels don’t use a reservoir, just the vacuum pump.

 

[Jnuehring]

The video describes the routing of the various vacuum lines. The title of your post said you lost the vacuum to the HVAC Controls and wanted to know where it is.

The black line behind the turbo goes through the firewall to the vacuum connector where the multicolored tubes, the vacuum harness, run to the control panel. They then go to the actuators. The “Vacuum Reservoir” is a carryover from gas trucks. The diesels don’t use a reservoir, just the vacuum pump.

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You may have saved the day. In July I gave my Utah born 1998 5.9L a face lift and put a 1999 California body on. in doing so I switched everything in the 1999 cab out and put all the 98 in, HVAC, Wiring Harness, etc. Somehow I must have pinched or pinned the line between the HVAC unit and firewall as I cannot get any play out of it, and I have no vacuum in the cab. I have seen the above diagram, but became confused by the black vacuum line going into and out of the clear vacuum coupler to the hVAC controls. If I understand your post the black line going into the coupler and to the HVAC control is the main vacuum feed line? I just watched a you tuber route a new line through the firewall grommet near the steering column and into the cab and hook it up to a black vacuum line. I just couldn't tell where he hooked it up too. thanks for your reply

 

[Jnuehring]

You may have saved the day. In July I gave my Utah born 1998 5.9L a face lift and put a 1999 California body on. in doing so I switched everything in the 1999 cab out and put all the 98 in, HVAC, Wiring Harness, etc. Somehow I must have pinched or pinned the line between the HVAC unit and firewall as I cannot get any play out of it, and I have no vacuum in the cab. I have seen the above diagram, but became confused by the black vacuum line going into and out of the clear vacuum coupler to the hVAC controls. If I understand your post the black line going into the coupler and to the HVAC control is the main vacuum feed line? I just watched a you tuber route a new line through the firewall grommet near the steering column and into the cab and hook it up to a black vacuum line. I just couldn't tell where he hooked it up too. thanks for your reply

so if a gas has a vacuum reservoir then a diesel just uses the vacuum line which normally feed through the fire wall on the passenger side.

 

[Jnuehring]

so if a gas has a vacuum reservoir then a diesel just uses the vacuum line which normally feed through the fire wall on the passenger side.

Thanks Scott..

 

[BigPapa]

Glad you got it working.

 

[Jnuehring]

I didn't yesterday, but did discover the cable (yes it has a cable (early 98) which controls the blend door). reattached that, ran new vacuum line through the firewall under steering wheel and it alll works. Except AC, I will be starting a thread for that. I had a retired master mechanic friend pull vacuum on the AC, held for some thirty hours, installed new dryer, o rings etc and new refrigerant. He was able to bypass (something and the pump ran fine if it was bypassed. My new issue..