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 08-15-2009, 10:03 PM
Bruester
 
Join Date: Jul 2007
Location: New Rochelle, New York
Posts: 13
A/C Compressor clutch stops after 10 min....why?

The air conditioning on my 1987 300TDT works great -- very cold -- for about 10 minutes after I start my car. Then the clutch on the A/C compressor disengages, causing the air to lose its cool. I have a 2 year old remanufactured compressor, and the AC (red) switch, expansion valve and dryer were replaced. I just recharged the system with a can of 134a (conversion was done by previous owner).

Any idea why the AC compressor clutch stops engaging after 10 minutes? It seems to happen when it's more than 85 degrees outside. Thanks

Reply With Quote
  #2  
Old 08-15-2009, 10:12 PM
bustedbenz's Avatar
Registered User
 
Join Date: Feb 2007
Location: Valle Crucis, NC
Posts: 2,283
I have the same problem. Very interested in what diagnostics turn up here.
__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL
Reply With Quote
  #3  
Old 08-15-2009, 10:32 PM
Registered User
 
Join Date: Sep 2001
Location: central Texas
Posts: 17,281
Do you have any way to put gauges on it ?
There may be a partial blockage and a high pressure cutoff switch... which would account for cold air but stopping after a little while...
However, I have no MB manuals for past 1985 and specialize in type one... around 1980 because the later ones are just too complicated for my simple mind....
So I do not know if you even have a high pressure cutoff switch... but gauges are a great place to start so you know more about what is happening inside the system....
Reply With Quote
  #4  
Old 08-15-2009, 10:33 PM
Registered User
 
Join Date: Sep 2001
Location: central Texas
Posts: 17,281
Does airflow through the center vents slow down to almost nothing before the clutch stops engaging ?
Reply With Quote
  #5  
Old 08-15-2009, 11:14 PM
LarryBible
Guest
 
Posts: n/a
On the 124 cars a sensor is on the rear of the compressor that senses compressor rotation. If lack of rotation is sensed, the clutch circuit is interrupted. Turning the igniton off and back on resets it.

The idea is to shutdown a failed compressor before it scatters metal throughout the system. Several things besides an internally failed compressor can cause the sensor to trip; a slipping belt, a slipping clutch or a worn compressor that allows the compressor innards to have excessive thrust.

Hope this helps.
Reply With Quote
  #6  
Old 08-16-2009, 10:13 AM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Quote:
Originally Posted by LarryBible View Post
On the 124 cars a sensor is on the rear of the compressor that senses compressor rotation. If lack of rotation is sensed, the clutch circuit is interrupted. Turning the igniton off and back on resets it.

The idea is to shutdown a failed compressor before it scatters metal throughout the system. Several things besides an internally failed compressor can cause the sensor to trip; a slipping belt, a slipping clutch or a worn compressor that allows the compressor innards to have excessive thrust.

Hope this helps.
As a follow-on to this, I would recommend eliminating the Klima circuit that monitors these various parameters as a test.

Pull the Klima and connect a jumper between sockets 5 and 7. The compressor will start. See if it continues to run past the 10 minute point. If it does, the problem is in the Klima..........one of it's parameters is not to spec.

If it doesn't........I'd be inclined to believe the evap temp switch is NG.

The real question is whether the compressor ever comes back online after it shuts down.........if it never comes back until a restart, the problem is most certainly with the Klima.
Reply With Quote
  #7  
Old 06-13-2010, 06:51 PM
tankowner's Avatar
You talkin’ to me?
 
Join Date: Dec 2007
Location: Columbia, MO
Posts: 907
In a search I came across this thread and was intrigued because my AC compressor clutch disengages after about 10 mintues. A few things I would note are:

1. I am not getting airflow through the center vents. Lethermang alluded to this, what's the deal -last year it was plenty of cold air through the center vents.

2. I don't suspect the Klima itself (because I replaced it a couple years back), but can do the 5 to 7 pin jumper to see what happens. However . . .

3. I should note that the compressor does seem to come back on sometimes after shutting down, and without having to shut down and restart the car. Even when it is on though, the air isn't freezing cold.

I am going to put some guages on tonight and will report back. But I am wondering if anyone has any thoughts. Thanks.
__________________
'95 E300D ("Tank") - 231,000 miles
'79 240D ("Biscuit") - 197,250 miles (Sold)
'83 240D ("Ding-Ding") - 217,000 miles (Death by deer)
______________________________________

"Back off, man. I’m a scientist” ~ Peter Venkman
Reply With Quote
  #8  
Old 06-14-2010, 12:20 PM
mach0415's Avatar
Diesel Weasel
 
Join Date: Mar 2010
Location: Lawndale, NC
Posts: 648
FWIW i have seen several A/C compressor clutches around here in NC (non MB, although it should still be the same concept) do the same thing. You can smack the center of the clutch with a pry bar and they work again for a little while and then quit. Two things come to mind:
1.) The air gap is set on the high end of acceptable parameter and with heat, it expands to beyond specs.
2.) Clutch coil is weak, due to high resistance. With heat comes higher resistance and eventual intermittent failure.

Do you know if there is a signal at the clutch coil (at the plug) after this happens?
__________________
Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi
Reply With Quote
  #9  
Old 06-14-2010, 12:48 PM
92 300D 2.5L OBK #59
 
Join Date: Feb 2007
Location: Central FL
Posts: 1,108
Quote:
Originally Posted by LarryBible View Post
On the 124 cars a sensor is on the rear of the compressor that senses compressor rotation. If lack of rotation is sensed, the clutch circuit is interrupted. Turning the igniton off and back on resets it.

The idea is to shutdown a failed compressor before it scatters metal throughout the system. Several things besides an internally failed compressor can cause the sensor to trip; a slipping belt, a slipping clutch or a worn compressor that allows the compressor innards to have excessive thrust.

Hope this helps.
I thought it was to save the belt considering one serpentine belt drives everything. From the CD 83-600.pdf
[IMG]file:///C:/Users/BOB/AppData/Local/Temp/moz-screenshot.png[/IMG]
Attached Thumbnails
A/C Compressor clutch stops after 10 min....why?-belt.jpg   A/C Compressor clutch stops after 10 min....why?-kilma.jpg  
__________________
92 300D 2.5L OM602 OBK #59
Reply With Quote
  #10  
Old 06-14-2010, 01:05 PM
LarryBible
Guest
 
Posts: n/a
Saving the belt is not a bad thing and I'm not sure what it's exact purpose was, but the function is the same.

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 05:01 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page