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 > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 12-23-2009, 11:16 PM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
SD climate control

I've got the SD back on the road after 18 months and am enjoying driving it.

During it's hiatus, it received a new auxiliary water pump and it's functioning properly.

The climate control system is also working properly with respect to all of its air doors..........all the pods are functional.

The issue is the temperature at the defrost outlets above the dash and the temperature of the center vents.

When the engine is fully warm.........90C.........the temperature of the air at the footwells is very warm.........and comfortable.

However, the leak air at the defrost outlets (using the economy button) is best described as cold.........not quite as cold as ambient (25F) but noticeable colder than body temperature.

The air from the center vents (vacuum on all the time) is also the same..........cold. I close the dash sliders to eliminate most of it.


The question that I have is for those who are intimately familiar with the airflow of these units. How can the system provide hot air to the footwells, hot air to the side window defrost outlets, cold air to the defrost outlets at the windshield and cold air to the center vents?

Appreciate it if WAG's are not part of the responses...........

Reply With Quote
  #2  
Old 12-24-2009, 02:05 AM
Custom User Title
 
Join Date: Jun 2008
Location: Simi Valley, CA (SoCal)
Posts: 454
I understand the nature of your question - How does cold air route through some parts of the system while hot/warm air is routed through other parts? You've caught me out of town without access to my manuals, and you don't want any WAGs, but how about a SWAG - a WAG of the Scientific variety?

My understanding is that the center vents are part of the A/C system, and the airflow through them is not routed across the heater core. Same with the vent to the rear seats. When the middle button is pressed, I believe air is routed through the center vents when the A/C is active, and through the side vents and leg flaps when the heat is active. The thing about the defrosters has me puzzled though. Most modern systems turn on the A/C when defrosting to remove humidity. I'm not saying the A/C is on, just that this is the portion of the system that would appear to be common to both. In Defrost mode, does the A/C'd air mix with heated outside air, or does the A/C'd air flow across the heater core? Not sure.

I'm thinking there may be a flap with a bad seal allowing A/C air or outside air into the ducting system, and with the flaps positioned for heat, the other vents are not sealed off from the outside air.

Put the temp control to max heat. Do the defrost vents blow hot in Defrost Mode? Do the center vents blow hot in A/C mode? From your description, I'd assume they are operating at least nominally. And what happens when the center button is pressed, do you get the same symptoms? Does the phenomena present itself only while you are moving or also while you are standing still?

Is there a diagram somewhere that shows the air flow ducting and the flaps controlling air flow through them?

My apologies if this is too much a WAG. It's always good to have someone to troubleshoot with and I hope my questions provoke responses that cause you to think in directions you may not have on your own.
__________________
mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)
Reply With Quote
  #3  
Old 12-24-2009, 02:35 AM
MBeige's Avatar
Registered User
 
Join Date: Apr 2005
Location: SoCal
Posts: 3,746
Isn't it that the MB engineers designed the climate control system so that the center vents only blow cold air, the side vents only blow warm/hot air, and when the side vents are blowing warm air but the system is not in defrost, then the defrost vents only blow lukewarm air (if at all)?
Reply With Quote
  #4  
Old 12-24-2009, 05:37 PM
Registered User
 
Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,164
I have the same symptoms but attributed it to the fresh/recirc door not closing fully. A portion of the pod(short throw) is leaking so the line is capped off. I've tried to match this symptom to what is shown on the schematic but there must be some differences in actual "physical" ductwork than what is shown. With that in mind, have you verified the fresh/recirc door is closing fully?

Also, what are you getting T/V mode?
__________________
Sam

84 300SD 350K+ miles ( Blue Belle )
Reply With Quote
  #5  
Old 12-24-2009, 05:55 PM
NoSparkNeeded's Avatar
Registered User
 
Join Date: May 2008
Location: Northern California
Posts: 509
Serendipity

Funny I was just thinking about center vents in my TD while driving home from work. Sometimes I feel air blowing strongly through the center vents. Sometimes not at all. The side vents however always blow air no matter what button or setting of the CC. People speak of the"pod" that controls these center vents. Can said pod function well intermittently? I'm not really sure when the center vents are supposed to blow as strongly as the side vents. Seems to me that they should be the same as the side vents at all times, but reading here indicates that isn't true. Has anyone done a write up on CC button selection vs. center vent "blowing"?I'm not really sure if I need a pod or if I just don't understand when the center vents are supposed to match the side vents.
__________________
85 300TD FED-Daily
84 300SD-Wife's
86 XJS-Sunday
66 GMC-Work- Given to my stepson
83 BMW Airhead- Given to my stepson

Last edited by NoSparkNeeded; 12-24-2009 at 06:27 PM.
Reply With Quote
  #6  
Old 12-24-2009, 06:24 PM
Craig
Guest
 
Posts: n/a
Quote:
Originally Posted by NoSparkNeeded View Post
Funny I was just thinking about center vents in my TD while driving home fromwork. Sometimes I feel air blowing strongly through the center vents. Sometimes not at all. The side vents however always blow air no matter whatbutton or setting of the CC. People speak of the "pod" that controls these center vents. Can said pod function well intermittently? I'm not really sure when the center vents are supposed to blow as strongly as the side vents. Seemsto me that they should be the same as the side vents at all times, but reading heretells me that isn't true. Has anyone done a write up on CC button selection/center vent "blowing"? I'm not really sure if I need a pod or if I just don't understandwhen the center vents are supposed to match the side vents.
In general, the center vents are only supposed to blow cold air. When you are in "heat" mode the center vents will be isolated. Some people have bypassed that function so the center vents are always open.
Reply With Quote
  #7  
Old 12-24-2009, 06:29 PM
280EZRider's Avatar
No Dumping
 
Join Date: Jul 2007
Location: Medford, OR
Posts: 1,451
MBeige is correct and, regardless of CC or manual, the center vents are for fresh or conditioned air only.
__________________

Don't Chrome them; polish them
Reply With Quote
  #8  
Old 12-24-2009, 06:40 PM
NoSparkNeeded's Avatar
Registered User
 
Join Date: May 2008
Location: Northern California
Posts: 509
fresh or conditioned air only

Then can "fresh" air be warmed air? Should in theory only A/C or ambient outside air blow through the center vents? I have felt warm air through the center vents with the heater on, even though it was cold outside.Has anyone done a "map" of the climate control settings, and what vent is supposed to be doing what, at each button setting, and fan speed? I might be having a stupid attack, however, I'm never real sure, in detail, what each button setting is supposed to do, when it's functioning properly. I use the "EC" setting mostly, and the defrost. I'm sure there was heh, "intelligent design" going on in the german engineer's mind, however I'd kinda like the center vents to do whatever the side ones are doing, at all times.
__________________
85 300TD FED-Daily
84 300SD-Wife's
86 XJS-Sunday
66 GMC-Work- Given to my stepson
83 BMW Airhead- Given to my stepson
Reply With Quote
  #9  
Old 12-24-2009, 06:55 PM
Custom User Title
 
Join Date: Jun 2008
Location: Simi Valley, CA (SoCal)
Posts: 454
Quote:
Originally Posted by NoSparkNeeded View Post
Has anyone done a "map" of the climate control settings, and what vent is supposed to be doing what, at each button setting, and fan speed?
Yes. It's in the FSM. That said, I gotta load the FSMs onto my wife's laptop.
Quote:
Originally Posted by NoSparkNeeded View Post
I might be having a stupid attack,
me too
Quote:
Originally Posted by NoSparkNeeded View Post
however, I'm never real sure, in detail, what each button setting is supposed to do, when it's functioning properly. I use the "EC" setting mostly, and the defrost. I'm sure there was heh, "intelligent design" going on in the german engineer's mind, however I'd kinda like the center vents to do whatever the side ones are doing, at all times.
As I've been told, the Mercedes engineers have millions of miles of experience with (your favorite topic here). Best not mess with it.

Now get off the damn computer and spend some time with your families. Merry Christmas!
__________________
mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)
Reply With Quote
  #10  
Old 12-24-2009, 07:14 PM
280EZRider's Avatar
No Dumping
 
Join Date: Jul 2007
Location: Medford, OR
Posts: 1,451
Quote:
Originally Posted by NoSparkNeeded View Post
Then can "fresh" air be warmed air? Should in theory only A/C or ambient outside air blow through the center vents? I have felt warm air through the center vents with the heater on, even though it was cold outside.Has anyone done a "map" of the climate control settings, and what vent is supposed to be doing what, at each button setting, and fan speed? I might be having a stupid attack, however, I'm never real sure, in detail, what each button setting is supposed to do, when it's functioning properly. I use the "EC" setting mostly, and the defrost. I'm sure there was heh, "intelligent design" going on in the german engineer's mind, however I'd kinda like the center vents to do whatever the side ones are doing, at all tyou are imes.
If you are feeling warm air thru the center vents when the heat is on, some warm air is naturally raising from the housing of the heat exchanger, which is below the fresh air duct, but if the air flow is measurable thru the center vents, then the vent flap is opening when it shouldn't be. And yes, I did some mental mapping the system many years ago when I replaced the CC for a manual system in my W123. Unfortunately, I forgot most of it when I said, "Good riddense" to the CC.
__________________

Don't Chrome them; polish them
Reply With Quote
  #11  
Old 12-24-2009, 08:56 PM
Custom User Title
 
Join Date: Jun 2008
Location: Simi Valley, CA (SoCal)
Posts: 454
Quote:
Originally Posted by Brian Carlton View Post
Appreciate it if WAG's are not part of the responses...........
How 'bout if the thread gets hijacked instead?
__________________
mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)
Reply With Quote
  #12  
Old 12-24-2009, 11:07 PM
MBeige's Avatar
Registered User
 
Join Date: Apr 2005
Location: SoCal
Posts: 3,746
Quote:
Originally Posted by MBeige View Post
Isn't it that the MB engineers designed the climate control system so that the center vents only blow cold air, the side vents only blow warm/hot air, and when the side vents are blowing warm air but the system is not in defrost, then the defrost vents only blow lukewarm air (if at all)?
I want to correct myself, the side vents blow hot and cold air. Center vents, only cold air. I was thinking, in heat mode, the side vents should blow heated air, while the center vents, if opened, blow cold air, even in heat mode.
Reply With Quote
  #13  
Old 12-25-2009, 12:34 AM
280EZRider's Avatar
No Dumping
 
Join Date: Jul 2007
Location: Medford, OR
Posts: 1,451
Quote:
Originally Posted by MBeige View Post
I want to correct myself, the side vents blow hot and cold air. Center vents, only cold air. I was thinking, in heat mode, the side vents should blow heated air, while the center vents, if opened, blow cold air, even in heat mode.
Agreed
__________________

Don't Chrome them; polish them
Reply With Quote
  #14  
Old 12-25-2009, 01:26 AM
MBeige's Avatar
Registered User
 
Join Date: Apr 2005
Location: SoCal
Posts: 3,746
Quote:
Originally Posted by Craig View Post
In general, the center vents are only supposed to blow cold air. When you are in "heat" mode the center vents will be isolated. Some people have bypassed that function so the center vents are always open.
Yes, I am one of those. The center vents in my W123 blow the same type of air the side vents blow out. Cold when cold on the side, hot when hot on the side. It has worked this way since the day I removed the center vent actuator or pod and routed the vacuum lines to each other (rather than to a 3-way connector that goes to the actuator/pod).

Removal of the center vent was necessary because the spring in the actuator kept the center vent flap closed (default). Removing the actuator/pod + spring allowed me to set the center vent flap to open.
Reply With Quote
  #15  
Old 12-25-2009, 11:49 AM
Registered User
 
Join Date: Jan 2006
Location: my own little world
Posts: 320
Brian...i had that problem on an old 126 I no longer have...put in a different controller and it was fixed.
I do have a 126 climate control manual...and at this time only one 126 thats apart for an engine swap....so if you want to borrow the manual youre welcome to it. Let me know.

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 05:42 PM.


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