Throttle cutout in Klima relay
08-01-2018, 07:38 AM
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Mercedes 300E 1990
Throttle cutout in Klima relay
Hi all,
I have an AC issue that is nagging me.
The AC is intermittent. It sometimes comes on - other times doesn't. There is no regularity in the pattern.
I have done a systematic diagnostic of the Klima relay (N6), and observed that the Full Load Throttle signal on pin 4 is very low, almost 0V.
According to the troubleshooting guide, this should only happen at WOT, so it suggests that the power to the compressor is shut off here.
The signal on pin 4 comes from the KE control unit (N3) pin 19, and I have have verified the connectivity between N3, pin 19 and N6, pin 4
The N3 unit takes the WOT signal from the Throttle Valve Switch, which I have also tested positive, as well as the connectivity between the pin 3 on the switch and pin 5 on N3, where it terminates.
If I do a bench test of N3 with 12V on pin 1 and Ground on pin 2, I get 0.09V on pin 19, consistent with what I read on pin 4 on N6.
I have now tested two N3 boxes, and they show exactly the same behaviour, so I doubt that this unit is defective.
I assume that N3 should show close to 12 V on pin 19 if it detects open loop (no WOT) on pin 5. If not, then the Klima test guide is wrong.
However, I cannot figure out if I am missing something obvious in my testing, or the subsystems are not interacting as I expect.
Unfortunately, the KE Injection System Test manual is covering various N3 variants, that doesn't seem to include mine - or at least not for the specific AC cutout test.
Is there any expert on these units in this forum - or someone who has been through this particular diagnosis before?
Car; Mercedes 300E, 1990, Engine: M103.983
BR
Viggo
I have an AC issue that is nagging me.
The AC is intermittent. It sometimes comes on - other times doesn't. There is no regularity in the pattern.
I have done a systematic diagnostic of the Klima relay (N6), and observed that the Full Load Throttle signal on pin 4 is very low, almost 0V.
According to the troubleshooting guide, this should only happen at WOT, so it suggests that the power to the compressor is shut off here.
The signal on pin 4 comes from the KE control unit (N3) pin 19, and I have have verified the connectivity between N3, pin 19 and N6, pin 4
The N3 unit takes the WOT signal from the Throttle Valve Switch, which I have also tested positive, as well as the connectivity between the pin 3 on the switch and pin 5 on N3, where it terminates.
If I do a bench test of N3 with 12V on pin 1 and Ground on pin 2, I get 0.09V on pin 19, consistent with what I read on pin 4 on N6.
I have now tested two N3 boxes, and they show exactly the same behaviour, so I doubt that this unit is defective.
I assume that N3 should show close to 12 V on pin 19 if it detects open loop (no WOT) on pin 5. If not, then the Klima test guide is wrong.
However, I cannot figure out if I am missing something obvious in my testing, or the subsystems are not interacting as I expect.
Unfortunately, the KE Injection System Test manual is covering various N3 variants, that doesn't seem to include mine - or at least not for the specific AC cutout test.
Is there any expert on these units in this forum - or someone who has been through this particular diagnosis before?
Car; Mercedes 300E, 1990, Engine: M103.983
BR
Viggo
08-01-2018, 01:42 PM
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Mercedes 300E 1990
08-01-2018, 07:16 PM
#4
Out Of Control!!
I think you are trying to diagnose the wrong module on your SKD Vietnam 124.030--------see the attached wiring diagram.
Plus I would also put a set of gauges on the system------what is the H and L bar.
Plus I would also put a set of gauges on the system------what is the H and L bar.
Last edited by Plutoe; 08-02-2018 at 11:00 AM.
08-02-2018, 01:47 AM
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Mercedes 300E 1990
What makes you believe that?
Which module do you suggest I test instead?
The logical procedure is obviously starting with the Klima relay (N6) and testing for all sensor inputs.
This is what I have done, and that lead to 0V on the 87Z (pin4) WOT input from N3.
That is why I am now testing N3
The diagram you attached also shows this connection. at the top.
BR
Viggo
Which module do you suggest I test instead?
The logical procedure is obviously starting with the Klima relay (N6) and testing for all sensor inputs.
This is what I have done, and that lead to 0V on the 87Z (pin4) WOT input from N3.
That is why I am now testing N3
The diagram you attached also shows this connection. at the top.
BR
Viggo
08-10-2018, 10:35 PM
#6
Member
I had experience hunting down an intermittent aircon problem. It cut out irregularly and would normally came back if you shut down the engine and restarted, but it would cut out again. Tried many solutions: temperature sensor cable, the in-cabin little fan, checked slipping belt, pressure valve, thermostat, etc. and even the aircon control unit. It turned out to the the relay. I missed it because it was a replaced new by the workshop, claiming that it was factory original. It wasn't, and from experience aftermarket relays are only good for a short time. You will have better luck finding a good used one. Try pull one from the breakyard and see if it would cure your problem. If so then find a Mercedes genuine relay (very rare and expensive now) for the peace of mind. The aircon cut out relay is being the battery in the engine bay.
11-01-2019, 12:30 AM
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W124, E250D, E220
SO, KLIMA relay to blame??
I had experience hunting down an intermittent aircon problem. It cut out irregularly and would normally came back if you shut down the engine and restarted, but it would cut out again. Tried many solutions: temperature sensor cable, the in-cabin little fan, checked slipping belt, pressure valve, thermostat, etc. and even the aircon control unit. It turned out to the the relay. I missed it because it was a replaced new by the workshop, claiming that it was factory original. It wasn't, and from experience aftermarket relays are only good for a short time. You will have better luck finding a good used one. Try pull one from the breakyard and see if it would cure your problem. If so then find a Mercedes genuine relay (very rare and expensive now) for the peace of mind. The aircon cut out relay is being the battery in the engine bay.
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11-01-2019, 09:45 AM
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Mercedes 300E 1990
I ended up replacing the Klima relay with a self-constructed relay consisting of two Ice-cube relays in series.
The two cubes exactly fitted in to the shell of the old relay after removing the circuitry, so I could neatly plug it back into the socket.
From outside you cannot tell what is inside.
The new relay bypasses the input from the compressor speed signal, which clearly appeared to be the culprit shutting off the compressor intermittently.
Now there is cooling every time I press the dashboard switch.
/Viggo
The two cubes exactly fitted in to the shell of the old relay after removing the circuitry, so I could neatly plug it back into the socket.
From outside you cannot tell what is inside.
The new relay bypasses the input from the compressor speed signal, which clearly appeared to be the culprit shutting off the compressor intermittently.
Now there is cooling every time I press the dashboard switch.
/Viggo
06-24-2020, 01:02 AM
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Mercedes w124
Wirring diagram for ac and fan, It is better to install Relay Clima instead of I have
Hi all,
I have an AC issue that is nagging me.
The AC is intermittent. It sometimes comes on - other times doesn't. There is no regularity in the pattern.
I have done a systematic diagnostic of the Klima relay (N6), and observed that the Full Load Throttle signal on pin 4 is very low, almost 0V.
According to the troubleshooting guide, this should only happen at WOT, so it suggests that the power to the compressor is shut off here.
The signal on pin 4 comes from the KE control unit (N3) pin 19, and I have have verified the connectivity between N3, pin 19 and N6, pin 4
The N3 unit takes the WOT signal from the Throttle Valve Switch, which I have also tested positive, as well as the connectivity between the pin 3 on the switch and pin 5 on N3, where it terminates.
If I do a bench test of N3 with 12V on pin 1 and Ground on pin 2, I get 0.09V on pin 19, consistent with what I read on pin 4 on N6.
I have now tested two N3 boxes, and they show exactly the same behaviour, so I doubt that this unit is defective.
I assume that N3 should show close to 12 V on pin 19 if it detects open loop (no WOT) on pin 5. If not, then the Klima test guide is wrong.
However, I cannot figure out if I am missing something obvious in my testing, or the subsystems are not interacting as I expect.
Unfortunately, the KE Injection System Test manual is covering various N3 variants, that doesn't seem to include mine - or at least not for the specific AC cutout test.
Is there any expert on these units in this forum - or someone who has been through this particular diagnosis before?
Car; Mercedes 300E, 1990, Engine: M103.983
BR
Viggo
I have an AC issue that is nagging me.
The AC is intermittent. It sometimes comes on - other times doesn't. There is no regularity in the pattern.
I have done a systematic diagnostic of the Klima relay (N6), and observed that the Full Load Throttle signal on pin 4 is very low, almost 0V.
According to the troubleshooting guide, this should only happen at WOT, so it suggests that the power to the compressor is shut off here.
The signal on pin 4 comes from the KE control unit (N3) pin 19, and I have have verified the connectivity between N3, pin 19 and N6, pin 4
The N3 unit takes the WOT signal from the Throttle Valve Switch, which I have also tested positive, as well as the connectivity between the pin 3 on the switch and pin 5 on N3, where it terminates.
If I do a bench test of N3 with 12V on pin 1 and Ground on pin 2, I get 0.09V on pin 19, consistent with what I read on pin 4 on N6.
I have now tested two N3 boxes, and they show exactly the same behaviour, so I doubt that this unit is defective.
I assume that N3 should show close to 12 V on pin 19 if it detects open loop (no WOT) on pin 5. If not, then the Klima test guide is wrong.
However, I cannot figure out if I am missing something obvious in my testing, or the subsystems are not interacting as I expect.
Unfortunately, the KE Injection System Test manual is covering various N3 variants, that doesn't seem to include mine - or at least not for the specific AC cutout test.
Is there any expert on these units in this forum - or someone who has been through this particular diagnosis before?
Car; Mercedes 300E, 1990, Engine: M103.983
BR
Viggo
