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 04-12-2011, 11:10 PM
Registered User
 
Join Date: Oct 2010
Posts: 6
95 W124 AC Compressor Not Engaging

Well, it got warm and the Benz is hot!

Checked AC high pressure switch and found continuity which says system should let compressor engage. Gage hooked up to low pressure side shows > 100 psig with compressor off at ~ 80 F.

Coolant temperature sensor has low resistance when cold and increases when hot to appropriate numbers.

Pulled relay and found there is power and the control switches call for the compressor to turn on.

Jump the compressor and it runs and air starts to blow cold.

Don't have voltmeter to measure low ac voltage so can't check voltage in speed sensor circuit but there is not resistance when the system is off.

Does this look like I need to have the compressor replaced?

Reply With Quote
  #2  
Old 04-13-2011, 07:29 AM
engatwork's Avatar
Registered User
 
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 13,648
Can you get some pressure readings with the compressor engaged?
__________________
Jim
Reply With Quote
  #3  
Old 04-13-2011, 08:02 AM
Registered User
 
Join Date: Jun 2007
Location: Waterloo Illinois
Posts: 1,336
Dont you have to have compressor running to get a good reading on the low side? The only time my compressor would not turn on is because I was low on 134 or R12, what ever you have in your car.
Reply With Quote
  #4  
Old 04-13-2011, 08:29 AM
Moderator
 
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Are you getting the GROUND command signal thru the low pressure switch to pin #10 of the klima relay connector?
__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator
Reply With Quote
  #5  
Old 04-13-2011, 10:54 PM
Registered User
 
Join Date: Oct 2010
Posts: 6
engatwork: I only jumpered the compressor for a short time and did hook up to measure the low pressure.

04 Diesel: I know you need to have the compressor running to get a good read on the low side, but the pressure switch continuity and pressure reading say I have some freon in the system so can't have a large leak or I would have lost everything over the winter when I did not use the car much and the AC less.

mbdoc: Yes, have ground through pin 10. Separately checked to make sure the wires aren't shorted to ground somewhere in between. Also get continuity through to coolant temperature sensor (and it has resistance that changes with engine temperature) and have continuity through push-button switch to klima so the switch is asking for the compressor to turn on.

Tom
Reply With Quote
  #6  
Old 04-14-2011, 04:40 PM
benzworldrefuge's Avatar
Registered User
 
Join Date: Apr 2011
Location: Bayshore, NY
Posts: 44
FWIW, A bad serp belt tensioner will cause the compressor to stall long enough for the RPM sensor to shut it off. If its borderline you won't notice the loose belt through any other failures. This may not be your problem but it is one of the situations that will trigger the KLIMA relay to drop the compressor signal. I think High engine temp sensor reading (whether correct or not) will also trigger the KLIMA to drop the compressor signal.
__________________

88 300e
89 300e
93 400e
93 500e
77 308 GTB
Reply With Quote
  #7  
Old 04-16-2011, 09:31 PM
Registered User
 
Join Date: Oct 2010
Posts: 6
Well, Took the car to the shop. They found a bad solder joint on the control wire to the compressor speed sensor. Repaired and now the AC works.

Had the freon checked. About 1 lb low and charged it back up.

Now if the weather would warm up a bit like last weekend where we hit 80. Today there was snow / sleet in the air.

Tom
Reply With Quote
  #8  
Old 04-17-2011, 02:14 AM
vstech's Avatar
DD MOD, HVAC,MCP,Mac,GMAC
 
Join Date: Mar 2006
Location: Mount Holly, NC
Posts: 26,835
great job from that a/c tech!
care to post your location, and the shop name that found it?
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
Reply With Quote
  #9  
Old 04-26-2011, 01:15 PM
Registered User
 
Join Date: May 2003
Location: Long Island, NY
Posts: 83
Same problem on '96 S420

I cannot get the AC compressor to engage on my '96 S420. There is sufficient 134 to call for clutch engagement. The problem is there is only 7.5 volts on the harness plug. This car doesn't have the same thermal circuit as '95 and older 140's. There is a 1.5 wire in the plug and a corresponding .5 wire at terminal 25 on the digital Control unit. Somewhere the amperage is increased to handle the clutch requirements. The wiring diagram only shows a connector at the bottom of the fuse box with the two wires mentioned above connected.

I can't imagine the skinny wire coming out of the control unit carrying enough current to engage the clutch solidly. Nowhere in the wiring diagram is the circuit going into and out of the base module where some heavy duty switching occurs.
__________________
Joe Tripp
Mercedes Club member since '76
Continuous Mercedes ownership since '64.
'93 300SD 111,000 miles. Now has '99 E300 engine.
'94 S350 77,000 miles
'95 S350 148,000 miles.
'96 S420 159,000 miles.With '99 606 Diesel. Sold
'99 S600 one of 14 imported. Sold.
'89 Bentley 8 40,000 mi. Sold
Reply With Quote
  #10  
Old 04-27-2011, 03:55 PM
pesuazo's Avatar
Registered User
 
Join Date: Oct 2002
Location: Near Raleigh, NC
Posts: 580
Quote:
Originally Posted by tommmm View Post
Well, Took the car to the shop. They found a bad solder joint on the control wire to the compressor speed sensor. Repaired and now the AC works.

Had the freon checked. About 1 lb low and charged it back up.

Now if the weather would warm up a bit like last weekend where we hit 80. Today there was snow / sleet in the air.

Tom
I just would like to know where is this control wire or solder joint, at the compressor?, at the CCU?

I remember years ago I had a similar issue (intermittent compressor engagement) on my now gone 300E, resoldering several points on the CCU fixed the problem, there were some obvious cracked joints...
__________________
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified
Reply With Quote
  #11  
Old 06-23-2011, 05:41 AM
Registered User
 
Join Date: Feb 2001
Posts: 171
Hi all,

Bought a 95 e320 in mint condition last week. Just about everything works except the a/c.

A little history on it:

previous owner states she replaced the compressor last year. A/C worked for a few months, then she garaged the car for the summer, and the a/c stopped working when she started driving again in october.

When I got the car, the compressor would work for 1~3 minutes in the morning. Then the fan would just blow regular air.

I took it to a garage that does a/c service and had them charge the freon. They verified that the vacuum is still good and that there were no leaks (pressure was good, they said).

The charge did not help. Still blowing regular air.

So i took it to another place, an auto shop that specilizes in electric and a/c. These folks traced the problem to a compressor relay that was not turning on the compressor. So i had the part replaced.

The a/c worked for 3 minutes. Then it stopped again.

After 3 hours of troubleshooting, it's getting dark. So the a/c specialist gave up and asked me to come back tomorrow.

They ended up not charging me the $140 they wanted to troubleshoot and fix the problem.

So i was driving the car back, and i turn on the radio. The radio display works, but no sound came out. And the minute I turn on the radio, the buckle-up sign came on instantly, along with the interior lighting next to the buckle-up sign.

The radio eventually came back on and the buckle-up sign went away. But that really gave me a scare.

The other funny thing was, the driver side window's 1-touch open function failed as well. But resumed working after a few repeated tries.

Any ideas?

I've so far had the compressor replaced, charged the freon, and replaced the compressor relay. The mechanic told me they've confirmed the thermostate working, along with a few other a/c parts that they confirmed weren't the issue.

I'm a bit weary about bringing the car back to this auto electric place and thinking maybe i should just bite the bullet and send it to the dealership to have it looked at.

Any suggestions are most welcome!!

Theo
Reply With Quote
  #12  
Old 06-23-2011, 07:42 AM
Registered User
 
Join Date: May 2006
Posts: 590
tommmmmmm, tell us where

Quote:
Originally Posted by pesuazo View Post
I just would like to know where is this control wire or solder joint, at the compressor?, at the CCU?
I'd also like to know where the bad solder joint was.

Tommmm, it's ok to look at the board even though your car is running without any problems- really!

Thanks.
Reply With Quote
  #13  
Old 08-01-2017, 03:49 PM
Registered User
 
Join Date: Jul 2017
Posts: 6
I need help on my Mercedes W124, I just had an engine swap from the Om603 to the Om606 and after that, the ac compressor is not engaging. The 606 came with a compressor without a speed sensor. My mechanic tells me the absence of the speed sensor is the cause. Is there anyway to have my compressor work normal? Or is there a special klima relay for that compressor? .
Reply With Quote
  #14  
Old 08-01-2017, 04:26 PM
Registered User
 
Join Date: Nov 2010
Location: TX
Posts: 3,978
Quote:
Originally Posted by Lucio View Post
I need help on my Mercedes W124, I just had an engine swap from the Om603 to the Om606 and after that, the ac compressor is not engaging. The 606 came with a compressor without a speed sensor. My mechanic tells me the absence of the speed sensor is the cause. Is there anyway to have my compressor work normal? Or is there a special klima relay for that compressor? .
the 1995 version of the om606 should have a speed sensor on the compressor, The later models (W210 ones) had the variable compressor which lacked a speed sensor and cannot work with the wiring of your car. The 1995 version compressor difference by eyeballing is 4 mounting bolts as compared to 3 bolts of the later versions found in the W210 chassis

Some lexus/toyota vehicles had a similar denso compressor but actually used a speed sensor and thermal cut switch on the back of it, It will take quite an effort on your side to get this working (piece mealing together a back plate and a benz compressor crankcase), I doubt a mechanic will want to do that for you as its not a boxed job which he can stand behind.

Or you can do some measurements and see if the older style 4 bolt compressor can fit on your engine.
__________________
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
  #15  
Old 08-02-2017, 06:19 PM
Registered User
 
Join Date: Jul 2017
Posts: 6
My ac compressor has no speed sensor. Can you tell me more about what you meant?

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 12:03 PM.


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