I have a 1985 Mercedes 190E with about 150,000 miles on it. The problem is with the climate control system - The air temperature from the vents remains the same no matter what temperature I set the dial to. If i set it to hot, it does not come out as hot as I would expect heated air too, set at cold, it is way to warm for Airconditioned air. It appears that all vent control work (I.E., middle vents, side vents, floor vents and defrost). I have read alot of threads on climate control problems and I found none that were described as this one. Any suggestions?

Could be dirty contacts in your adjustment wheel.

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Peach Parts W124.128 User Group.

80 280SL
85 300SD
87 300TD
92 300D 2.5 Turbo
92 300TE 4Matic

I pulled the CCU unit out, all the solders seemed ok and there was no reason for me to believe there were dirty contacts. I believe the problem has something to do with the compressor.

I first noticed a clicking noise today, and it appears to be coming from the compressor. (It looks like the clutch is not engaging). I tried jumping the low pressure switch to see if it would cause the compressor to engage however showed no difference. I tried charging it with some R134, however it caused the fuse to blow all together. Any other ideas?

I think I am getting closer to the problem. Spent several hours trying different things and trying to narrow down the problem. Here is what I have so far.


1.)In regards to the previous post, the strange clicking noise is unrelated apparently and is not the compressor
2.)The compressor kicks in a few seconds after starting the car (evidenced by watching it and also seeing a slight RPM drop as it kicks in). It however a few seconds later it either -
a.) Blows fuse #1 (seems to only happen with blower on high)
b.) Kicks out and RPM's return to normal. I cannot seem to get it to cut back on again even for a short time unless i shut the car off and restart it.


Any reccomendations?

Check the Klima relay (a/c relay), it's located on the passenger's side fire wall with the fuel pump relay & the ECU. Access through the engine compartment it's covered by a plastic bezel. You can swap with a known working relay just to test it.

Ok, Ive pulled the klima relay. I am going to try and test it tomorrow. Do you have any advice on the best way to test it? What is the best way to determine if it is the klima relay it self or one of the relays inputs?

Sounds like either the compressor speed signal or the engine speed signal is faulty or the Klima relay is faulty.

If your Klima relay is similar to my 87, 260E, here are step by step instructions to get you going (steps 32 onwards would be particularly relevant):

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 auto modes, 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.

This is awfully long and I may have missed some possibility, but you will have enough info to test this problem in a systematic manner and when you come to a point where you think something is missing, let us know, some one will help.

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Saumil S. Patel

The pin diagram for the Klima relay connector is in this page:

http://www.peachparts.com/shopforum/showthread.php?t=158591&page=6

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Saumil S. Patel

The pins or slots are not numbered on the relay or where it plugs in? Is it numbered from top to bottom, left to right? Do holes without pins count in the numbereing? There are 9 pins on my relay Below is a simple diagram a - indicates no pin


o o o o - o
o o - - o o

I get three of them putting out battery voltage when running.

are you trying to put R134 refrigerant in a system that was designed for R12? Has the system been converted? Has it ever worked properly since you've had the car?

The AC has never actually worked since we got the car. We were uninvolved in the conversion but have been told it was converted for 134. Is there a way to tell if the conversion was done properly?

The pin numbers on the relay on my 260E are different from those on the socket. In the procedure I outlined, the pin number refers to those on the socket and they should run from 1 thru 12 interleaved between the two rows of 6 pins. The diagram tells you where to start when numbering them. Someone could tells us whether the two Klima relay (87, 260E & 85, 190E) are similar in their terminal assignments or not. But if you do find similarities as you go along the procedure, the assumption of similarity becomes atronger and stronger, so just try it.

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Saumil S. Patel

Thanks for the prompt reply. I got a little more troubleshooting information, not sure if it will help. I checked the voltage going into the low pressure cutoff swtich and it was battery. Coming out is next to nothing so i jumpered the switch. The compressor kicked on and ran for probably 30 seconds before fuse #1 blew. I will be hooking the AC pressure gauges up here in a minute but was wondering is that the expected outcome if you run the compressor with low pressure (blowing the fuse)?

Yes, possible, if it is too low, the compressor will tend to sieze. If the system is virtually empty, would need to evacuate and recharge, make sure you also add some oil when you recharge. The pressure switch is open possible because of low pressure. If the fuse blows even after you have recharged the system, the compressor clutch coil may be shorted. Infact, check the resistance of the compressor clutch coil (with car off), it should be between 2.5 and 3 ohms, anything lower could indicate a coil short.

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Saumil S. Patel

Ran out of time to work on it for the weekend. However wanted to post this in case somebody else came looking.

When referring to the mercedes benz repair manual and troubleshooting guide in relation to the KLIMA control box, it refers to them by pin number. I spent some time troubleshooting and putting it together but finally figured out which pin was which.

^ ^ ^ ^ ^
towards front passenger seat

1 5 7 9 11
______________
o - o o o o
o o - - o o
----------------
2 4 10 12

(note, the numbers reference the socket pin holes after the kilma relay has been pulled)
This again was for a 1985 mercedes 190E.