I did not know that the test is performed all the time, and all the time makes sense because the compressor could sieze any time, but once compressor is shutoff does the car not need to be turned off and then back on for it to work again ? Is it possible that your Klima relay has failed in some very desirable way, atleast for some ?

So then the problem may still lie in the speed sensors. You can test the speed sensor outputs at the Klima relay socket. somewhere in this thread I have the steps to test the sensor signals.

Or may be the relay itself, but check that shorting pins 5 and 7 gets rid of the problem.

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Saumil S. Patel

On page 6 of this thread, there is a layout of the Klima's socket.
Page 5 has the steps to test various cut-off mechanisms

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Saumil S. Patel

I too was surprised when it came back on without a restart. I've always heard it is not supposed to, but it always comes back after a few minutes. I've had to replace the relay before, and it still does the same. That's on a '90 124.

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2012 E350
2006 Callaway SC560

What's the part number of the Klima relay?

Sixto
87 300D

A/c comes at 1500 to 2000 Rpms & when the Rpm drops below 1500 rpm air still comes from the vents but not cold. Please help me to know what could be wrong.I donot have any Relay Diagram to follow the instructions.

If it gets warm under 1500RPM, maybe it is simply undercharged.

The question is, IS THE COMPRESSOR STILL RUNNING when the air gets "not cold."

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2012 E350
2006 Callaway SC560

I checked the system is fully charged & its not blowing any fuses either.You said jump the #5 & #7 inthe Klima relay socket I did & compressor engages.

Thanks

I jump the #5 &#7 the compressor came on & the a/c is working fine & there is not any rpm discrepecency.
1.This car does not have copper in 12 pin socket it means there is not ant hot temp switch.
2.I checked trotle switch circut by using positive battery terminal & pin 4, no voltage.
3 Checked the compressor speed sensor I got 650 resistance & .3v ac at idle.
4. Checked the engine speed sensor got 7v ac but voltage did not increase with engine rpm increase.
5. Might be klima relay bad.
Can I jump the #5 & # 7 in the relay & put the relay back in the socket & run for a while because I am just by passing the sensors.

Is anybody there to answer the above question?

You can't jump #5 and #7 and leave it that way because the compressor will never cycle.

You can, however, get a small "ice cube" relay and operate the relay using the ground from socket #10. This is the signal from the CCU. When the CCU closes the coil in the relay, then the load contacts will close and you'll let the relay effectively jump #5 and #7. #5 and #7 are the load contacts.

The compressor speed sensor looks o.k. BUT the engine speed sensor's output does not make sense. This is a diesel w124 right ? The voltage should be around 4V at idle and should increase with increase in RPM. The fact that you have a higher constant voltage means that at lower RPMs there is a discrepency between compressor and engine speeds and as the RPMs increase, the Klima expects a higher voltage from the engine sensor which is what it gets, so the compressor works. And what we can also predict is that at much higher RPMs the compressor will cut off again because now the Klima expects a voltage higher than 7V from the engine sensor. I would try to replace the engine speed sensor before replacing the Klima relay.

Also as Brian says, you can put an external relay which can be triggered by the terminal 10 in the Klima relay socket, this pin is grounded when the a/c needs to come on and is a signal that originates from the climate control box. Here is the scheme.

Attached Files

Bypass Klima.pdf (11.2 KB, 276 views)

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Saumil S. Patel

The engine is 603 & where I can buy this small ICE Cube relay or what is going to be the part #. Is Hastings is good brand for oil,diesel filters or which brand I should use for the filters. what brand engine oil I should use for 350sd. Do you guys like Shell 15w40.I live in South Tx(Hot) temp.

You can buy this at Radio Shack.

http://www.radioshack.com/product/index.jsp?productId=2062482&cp=&sr=1&origkw=relay&kw=relay&parentPage=search

You want to use a relay which has the lowest coil current spec (the mini relay at the above site looks ideal to me) and a contact current spec greater than 10A. The compressor will draw a maximum of 4.5-5A, the extra amps in the spec is to account for poor construction of parts now-a-days.

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Saumil S. Patel

Where this relay is going to fit, I mean in the same sockect where klima relay goes & which pins it will go in.

This relay will not fit in the Klima socket. But your question made me think again, and infact, you should be able to do a bypass operation inside the Klima relay itself. Do you consider yourself a good electrical person ?

The relay can be opened by just cutting (using a blade cutter) all the way around the 4 edges where the relays pins are coming out from. You would see glue all around and that is what you are trying to cut. Once the edhes are cut, the cover will seperate from the board, the board is attached with the terminals of the relay.

Once you have opened it, the terminal on the board corresponding to socket's terminal 10 can be identified. Just scrape the copper around this terminal on the board, i.e. isolate the terminal from the rest of the circuit. Now locate the terminals of the coil of the relay. Isolate these terminals from the rest of the circuit by cutting copper around them also. Double check all the isolations using a multimeter. Those isolated terminals should not beep with any other parts of the circuit.

Now solder a wire FROM the terminal corresponding to socket's terminal 5 on the board TO one of the isolated relay coil terminal. Next, solder a wire FROM the isolated terminal corresponding to socket's terminal 10 TO the other isolated relay coil terminal.

Make sure that there are no accidental shorts. Then insert the relay car into the socket to test that your bypass actually worked.

You can now put the board back into the cover and using a glue gun, seal it.

It is possible that such a relay is readily available, I dont know the source. If you are not comfortable with electronics, send it to me, I will gladly do it for you.

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Saumil S. Patel