Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 05-24-2012, 09:57 PM
Registered User
 
Join Date: Mar 2000
Posts: 534
W124 HVAC Vacuum Supply Issue

1990 E300 D 2.5... A/C and heat work but regardless of the the pushbutton control unit setting, the vast majority of the air is directed to the defroster vents.

The HVAC system derives it's vacuum from the brake booster vacuum line, via a brown plastic hose. Vacuum is present in the booster vacuum line.

The brown vacuum supply line enters the cabin through a firewall grommet on the driver's side. Where does this brown vacuum supply line connect to the HVAC system? On the right side of the heater box? Its not visible with the instrument cluster, PBCU and glove box removed.
Reply With Quote
  #2  
Old 05-24-2012, 11:09 PM
Aquaticedge's Avatar
Bump on a log
 
Join Date: Nov 2009
Location: See Biography
Posts: 3,148
you likely have several Dash vacuum pots out of sorts. Your supply line goes to an electronic gang valve if it's the typical W124 Setup. the main line should be green... brown is generally they key cyl if I recall right. the default system with errors is Defrost

The electronic valve should be on the right hand side of the HVAC box where the glove box is, theres a retention pin in the bottom and a place where it snaps into place on the box, but it may have jarred loose, I will post several pictures in a moment
__________________
hum.....
1987 300TD 311,000M Stolen. Presumed destroyed
Reply With Quote
  #3  
Old 05-24-2012, 11:22 PM
Aquaticedge's Avatar
Bump on a log
 
Join Date: Nov 2009
Location: See Biography
Posts: 3,148


__________________
hum.....
1987 300TD 311,000M Stolen. Presumed destroyed
Reply With Quote
  #4  
Old 05-24-2012, 11:24 PM
Aquaticedge's Avatar
Bump on a log
 
Join Date: Nov 2009
Location: See Biography
Posts: 3,148
Note, I have the HVAC box top OFF so your setup should look a little more complete then this. chances are it's your footwell pods or the Central Control Valve. Buy a mighty vac, It will soon become your best friend diagnosing the system. if you have to do the central Pod, you might as well replace all of them while your there, it's about 100.00 or so in parts, but it's also peace of mind
__________________
hum.....
1987 300TD 311,000M Stolen. Presumed destroyed
Reply With Quote
  #5  
Old 05-25-2012, 09:10 AM
Registered User
 
Join Date: Mar 2000
Posts: 534
Thanks for the photos... exactly what was needed. The M-B W124 ACC service files consist of photocopies of the original documents and image quality is rather poor.

I stand corrected on the brown vacuum supply line - that is for the fuel shutoff element.

What needs to be checked first is the green/yellow vacuum supply line. The entire heater box was renewed a couple of years ago to address a leaking evaporator problem. The new box included all new vacuum elements, so I'm hoping that the elements are not the issue. The electric gang valve is factory original (1990) so that will been inspected next should the vacuum supply prove to be intact.
Reply With Quote
  #6  
Old 05-25-2012, 09:18 AM
Registered User
 
Join Date: Nov 2010
Location: TX
Posts: 3,578
The main HVAC vacuum line is green and is teed a yellow funnel looking piece behind the brake booster, check there first.
__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
Reply With Quote
  #7  
Old 05-25-2012, 10:39 AM
Registered User
 
Join Date: Mar 2000
Posts: 534
Fixed!

Traced HVAC vacuum supply line to 3 way splitter from vacuum pump; isolated HVAC supply circuit and HVAC worked properly. Added remaining vacuum circuits individually until HVAC reverted to Defrost mode. Traced vacuum circuit that resulted in the HVAC defrosting and found cracked rubber vacuum line connector below air filter housing bleeding air into the system. Renewed connecter, vacuum level returned to normal and everything is functional again.

Guys, thanks for your help!
Reply With Quote
  #8  
Old 05-25-2012, 03:54 PM
Aquaticedge's Avatar
Bump on a log
 
Join Date: Nov 2009
Location: See Biography
Posts: 3,148
Quote:
Originally Posted by jgl1 View Post
Fixed!

Traced HVAC vacuum supply line to 3 way splitter from vacuum pump; isolated HVAC supply circuit and HVAC worked properly. Added remaining vacuum circuits individually until HVAC reverted to Defrost mode. Traced vacuum circuit that resulted in the HVAC defrosting and found cracked rubber vacuum line connector below air filter housing bleeding air into the system. Renewed connecter, vacuum level returned to normal and everything is functional again.

Guys, thanks for your help!
Awesome! Congrats on the fix!
__________________
hum.....
1987 300TD 311,000M Stolen. Presumed destroyed
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 01:21 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page