E300d S124 Aircon Problems

Defector

New Member
Joined
Aug 16, 2005
Messages
9
Reaction score
0
OK. so i got my E300d estate on the road last week with a new MOT and it runs well apart from the air con.
I believe that it has a genuine mercedes aircon system with the EC button.
The problems are thus:

The auxilliary air con fan is running constantly on fast speed when i switch ignition on - there is only one fan although everywhere i search there appears to be two fans on the front of most cars.
For this i have checked the secondary aux fan relay (behind fuses) and it appears to be functioning correctly with no burned points and clicks on and off correctly.
The wiring to the connector on the temperature switch on the front of cylinder head was shorting near the connector so i insulated them correctly but still no joy.
I removed the Klima relay but the fan still roars into action with ignition on.
I shorted (in turn) the connectors on the reciever/dryer, but still the fan comes on.

I am now at a loss as to what else to try.
I am not getting any cold air from the aircon as the clutch will not engage, i had the car at kwik fit yesterday and after gassing, the aircon would still not function, so i also have to see where the problem for this lies.
I shorted pins 87 and 15 (i Think) on the Klima relay but clutch still will not engage.
Can i put a live feed direct to the clutch and if so is there a connector on clutch wiring as i cannot see one, just seems to be a wire going into the loom.

Any wiring diagrams would be helpful (1994 S124) and any other suggestions please.

I would prefer not to go to a specialist as am sure i would be raped and pillaged by them before it is completely fixed.

HELP
 
Last edited:

mej

Senior Member
Joined
Apr 17, 2011
Messages
430
Reaction score
3
Location
IoM and Languedoc
Your Mercedes
S124 1994 OM606, ditto OM605, ditto M111, W126, S211, W169
The diesels (such as my '94 OM605) only have one electric a/c fan. Try this (not my write up) which may help............. See step 27 particularly.

1. Turn Car Off
2. Pull Klima Relay Out
3. Put your multimeter on DC Volts setting
4. Connect the ground terminal of the meter (black color usually) to the battery's negative terminal
5. Connect the positive terminal of the meter to pin number 5 in the socket (Hopefully, you know which pin is 5)
6. You should get close to 12V, if not, the fuse is blown (#7 I think). Replace fuse. Put the Klima relay back in and check a/c again.
7. If the fuse is o.k. and the compressor clutch still does not run, then lets move on
8. Remove the Klima relay. Now connect the negative terminal of the meter to pin number 10 in the socket. (Hopefully you know which is pin 10). Put the positive terminal of the meter on the positive terminal of the battery.
9. Turn on the car and press one of the a/c switches on the push button unit.
10. You should get close to 12V when the a/c switch is on.
11. If you dont get close to 12V then there are one of two possibilities:
a. the push button unit is not sending the correct control signal
b. the pressure switch is not closed
For now, I am ignoring the trivial possibilities that wires or connectors may be broken. We can dive into these once we have some answers to the basic tests.
12. Turn the car off.
13. If you dont get the 12V, disconnect the two cables from the pressure sensor (should be at the drier), and jumper them.
14. Repeat steps 9 and 10.
15. If you still dont get the 12V, the push-button unit is not sending the signal.
16. Turn car off, dont keep the car running for a long time with the pressure switch cables jumpered.
17. If at step 14, you did get 12V, then the pressure switch is not closed
18. If the pressure switch is not closed there could be three possibilities:
a. refrigerant pressure is too low (lower than 2 bar)
b. refrigerant pressure is too high (higher than 30 bar)
c. the pressure switch is bad
you will need pressure gauges to seperate these possibilities.
16. If at step 11, if you did get 12V, then the push-button unit is sending the control signal and the pressure sensor is o.k. and we will move on.
17. If push-button unit is sending a signal and the pressure sensor is o.k. but the compressor clutch will still not run, then need to check the compressor clutch coil resistance.
18. Connect the positive terminal of the meter to pin number 7 in the socket and negative terminal of the meter to negative terminal of the battery.
19. Change the setting of the meter from volts to ohms.
20. You should get a low resistance about a few ohms.
21. If you don’t get a low resistance, need one last test.
22. Get to the compressor and disconnect the connector for the compressor clutch coil (there is a speed sensor cable that connects to the compressor connector also, you have to trace the clutch wire to the compressor connector to pick the right pin on the connector).
23. Put one of meter’s terminals on battery ground and the other terminal on the compressor’s clutch coil pin (polarity does not matter).
24. You should get a low resistance, about a few ohms. If you do get the low resistance at the compressor then compressor clutch coil is o.k.
25. If you get low resistance in step 23 but do not get a low resistance in steps 18-19, then the cable from the Klima relay to the compressor is bad, replace it.
25. If you don’t get a low resistance in step 23, then the compressor coil is open, normally this would require a new compressor.
26. If the compressor clutch coil is o.k. and the cable from the Klima relay to the compressor is o.k. then let us move on.
27. At this point, if the fuse is o.k., and the compressor coil’s resistance and cable are o.k., then jumper pin number 5 and 7 in the socket.
28. Turn on the car and your compressor should come on.
29. Turn car off
29. If the compressor does not come on, there are two possibilities:
a. the fuse is blown
b. the compressor has an internal mechanical problem, is likely seized.
30. No matter whether it is 29a (shorted coil) or 29b (seized), compressor is bad, replace it.
31. If the compressor comes on at step 28, but does not come on when the Klima relay is put back in and the push button switches are on a/c, then the Klima relay is not producing the 12V signal at its pin 7 to drive the compressor.
32. If Klima relay is not driving the compressor at step 31, then there are five possibilities:
a. the temperature sensor is bad
b. faulty throttle cutout microswitch (only for diesel automatic)
c. bad compressor speed sensor
d. bad engine speed sensor
e. bad Klima relay
33. Put the meter back on voltmeter setting. Do this test with engine cooler than 105 deg-C, better when just cold.
34. Put the positive terminal of the meter on the positive terminal of the battery. Put the negative terminal of the meter in pin 12 of the socket.
35. If you get about 12V, then the temperature sensor is bad. I am not sure about the physical location of this sensor but on my 87 260E, it is a 3 pin sensor on the engine I think third from last from the windshield side. You can ask your parts vendor about it.
36. If the temperature sensor is bad, then disconnect the sensor cables, put the Klima relay back, and try you’re a/c. If this was the only bad component, your compressor should start working. But again, don’t keep running like this, replace the sensor as soon as you can. If disconnecting the temp sensor cable does not work, there is still another problem. Remove the Klima relay and move on.
37. Put the positive terminal of the meter on the positive terminal of the battery. Put the negative terminal of the meter in pin 4 of the socket.
38. If you get about 12V, then the throttle cut-off switch is bad. This switch is supposed to be open and only close when the throttle is wide open. I am not sure about the physical location of this switch but you can ask your parts vendor about it. Once again, if you can find this part, you can disconnect the wire, put the Klima relay back and check a/c. If it still does not come on, then there is some other problem and move on.
39. Change the meter setting to measure resistance.
40. Put the positive terminal of the meter on pin 9 of the socket. Put the negative terminal of the meter in pin 11 of the socket.
41. You should get about 350 – 450 ohms. If you don’t get the low resistance but get very high resistance, either the compressor speed sensor is open circuit or the wire is broken somewhere. Do the same test as close as possible to the speed sensor (i.e. on the compressor connector) to rule out a broken wire. Replace sensor if it is bad.
41. If the resistance is o.k., then, jumper pins 5 and 7 on the socket.
42. Change the meter setting to ac volts.
43. Turn on the car.
42. You should get about 0.3V ac at idle of about 750 rpm. If you don’t get the ac voltage, and the resistance was kind of o.k., replace the sensor.
43. Turn off the car.
43. To check engine speed signal, put the meter setting to ac volts
44. Connect one terminal of the meter to pin 1 of the socket and the other to pin 2 of the socket.
45. Turn the car on.
46. For diesel: At idle of about 750 rpm, you should get a voltage greater than about 4V ac. And the voltage should increase with increase in RPM. For gasoline: at idle the voltage should be about 9V.
47. Stop the car
48. If you don’t get the voltage, switch the meter to resistance setting and readout the resistance between pins 1 and 2 of the socket.
49. You should get about 2 Kohms. If you get a very high resistance, check the resistance closer to the sensor to rule out a cut in the cable. Otherwise replace the sensor. Ask the parts person about its location.
50. If in step 15, you determine that the push-button unit is not sending the control signal, replace the push-button unit. This has happened to me once, the electronics driver inside the push-button unit is blown and it will not send the control signal to the Klima relay. What I did is bypassed the electronics and just used the mechanical switches to send the control signals. The downside is that there is no more automodes, so when I feel like it is too cold, I would press the economy switch and I designated that switch to send a signal to cut-off the compressor. So my brain does what the box would otherwise do, have still not fixed the electronics, just a big headache to test this unit once it is out of the car. If you just bought a new one, you can ask for a replacement. Most likely the problem you are having is not in that unit.
 
OP
D

Defector

New Member
Joined
Aug 16, 2005
Messages
9
Reaction score
0
  • Thread Starter
  • Thread starter
  • #4
Thanks very much for your replies, i will digest and start to do the relevant checks in the next few days.

I did spin the compressor by hand at the clutch and it does appear to turn easily and smoothly.
 
OP
D

Defector

New Member
Joined
Aug 16, 2005
Messages
9
Reaction score
0
  • Thread Starter
  • Thread starter
  • #5
Ok, so i think i have found out why my auxilliary AC fan is running at full tilt all the time. There appears to be a short in the two wires from the thermister on the cylinder head into the wiring loom as the fan engages/disengages when i push and pull the wire gently.
I have unwrapped the wires up to wher it goes into the loom trunking and although the insulation has also broken down here, the short appears inside the trunking.
This unfortunately is a manifold off job, but i am at least grateful that i know what the problem is.
Once i get this sorted, onwards and upwards to check out the rest of the problem with the AC:shock::confused:
 

Bolide

Senior Member
Joined
Sep 17, 2002
Messages
3,294
Reaction score
4
Website
www.w124.co.uk
Your Mercedes
BMW 525 Diesel Touring
There's not much wiring in the engine bay of an E300 Diesel so I'd replace all of it under the manifold. It will all be in a bad state

Nick Froome
 
OP
D

Defector

New Member
Joined
Aug 16, 2005
Messages
9
Reaction score
0
  • Thread Starter
  • Thread starter
  • #7
Still not had time to sort AC as need the car during the days:confused:.
Had a go at changing the pollen filters, after so much reading as to wether my car actually had pollen filters, i decided it must have as the air coming through the vents seemed restricted for the fan speeds.
There is a fantastic video on Youtube where an American goes through a thorough strip and replacement of the pollen filters on a W124.
After watching this video i reckon it took only 20 to 25 minutes for me.
The pollen filters were absolutely filthy and black as if full of soot, which leads me to believe it either has never been changed or not for a very long time.
Anyway with my hayfever, this change was important:):D
 
OP
D

Defector

New Member
Joined
Aug 16, 2005
Messages
9
Reaction score
0
  • Thread Starter
  • Thread starter
  • #8
before i threw away my pollen filters, i checked the sides of the filters and they had the genuine Mercedes logo's etc.
There were also markings for the month and year of manufacture.........08/94:shock::shock:

So these were the same filters that were in the car when it left the production line some 19 years ago, and in the meantime this car has had some major services by Mercedes dealers................not so major methinks.
Anyway, good job i never trust a garage to do any work on my cars, i do all my own maintenance and servicing.:D
 


AMF Automotive - We are an independent Mercedes-Benz and AMG specialist located in Paddock Wood, Kent, with full Mercedes Diagnostic equipment. We offer a full portfolio of tuning options for AMGs and can cater for all your Mercedes needs.
Tel: 0203 384 4644www.amfmercedes.com/
Top Bottom