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Green S Class s280 w140
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Discussion Starter #1
I have a 1996 w140 (my first Mercedes). It runs well and is mechanically sound but I think there is a problem with the aircon.

The EC light came on this weekend and it cant blow cold air on LO temp mode. I realise this may mean regassing the refrigerant but does it indicate there is a leak or a more serious problem. I know there are diagnostic codes for the system but not sure what they mean.

Any clues or advice appreciated.

There is local indie mechanic in my town who has a good rep but havent used his services before.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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the only proper way is to get fault codes from your AC. You can write them down and somebody will explain them to you. there are two tests for AC, please perform at least the first one where you can read refrigerant pressure and temperature and it will be much more clearer than now.
 

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SEC 600 V12 2dr COUPE (RHD) One of the chosen few.
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Dunedin been there.. Nice place.. Try a look on the Knowlege base the test sequence should be there..There are two types of AC control.. you need the test sequence for your type.. The CE light.. might be nothing to do with your AC..
 

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'07 CLK350
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Here's how to access the fault codes on your A/C:

Set the left temp selector to "HI"
Set the right temp selector to "LO"
Ignition off
Ignition on
Press REST + EC together for more than 1 sec
Recirculation light starts blinking, system does a short diagnostic and then will display error codes. Cycle through them with left and right AUTO buttons.

E FF Indicates the end of the list. If it is the first one you see then there are no error codes logged.


Here's a good link too. Technically its for E-Class cars but the A/C system software is the same:

How to Diagnose Air Conditioning Malfunctions | EclassBenz.com
 

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Green S Class s280 w140
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Discussion Starter #6
I have run the diagnostic using the above intructions. The only DTC code that displayed was B1241 which means Refrigerant fill in Chart 3. This information combined with the low bar pressure reading for the refrigerant from Actual values test leads me to conclude there is either a leak or it is time for new coolant.

There were no other error codes displayed during the DTC test. After doing the diagnostic and restating the car the EC button light turned off and stayed off.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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I have run the diagnostic using the above intructions. The only DTC code that displayed was B1241 which means Refrigerant fill in Chart 3. This information combined with the low bar pressure reading for the refrigerant from Actual values test leads me to conclude there is either a leak or it is time for new coolant.

There were no other error codes displayed during the DTC test. After doing the diagnostic and restating the car the EC button light turned off and stayed off.
What are the values for the pressure?
 

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Green S Class s280 w140
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Discussion Starter #8
Sorry i should have mentioned that earlier:

The sensor readouts from the actual values test were:

1. In car temp sensor - 21
2. Outside temp sensor - 16
3. heater core temp sensor (left) - 48
4. heater core temp sensor (right) - 28
5. Evaporator temp sensor - 17
6. ECT sensor - 54
7. Refrigerant pressure (bar) - 2
8. Refrigerant temp sensor - 17

Note: all temp readings in celsius

I repeated the diagnostic test 4 times while engine running but the coolant pressure remained at 2 bar (the temp readings changed as the car warmed up).

After running the above test 4 times I then commenced the fault code test or DTC test.

This returned only one error code: B1241 which confirmed low coolant pressure. I didnt run the flap test. Tommorrow the car goes in for a service. The old freon gas will be removed and new refrigerant will be added with fluorescent dye to test for any leaks.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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B1241 which confirmed low coolant pressure.
you mean refrigerant pressure.

Yes, 2 bar is low. consequently the temperature is too high. it should be below 5°C. But if you have a leak then most probably it is at an evaporator. Please report, I am afraid of that day on my car .... but almost for sure it will come.
 

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Green S Class s280 w140
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Discussion Starter #10
leak test done , new refrigerant added, bar pressure now 7. cold air now comes through on lo mode. Seems fine now but will keep an eye on it by repeating the full function test later.
 

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Green S Class s280 w140
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Discussion Starter #11
you mean refrigerant pressure.

Yes, 2 bar is low. consequently the temperature is too high. it should be below 5°C. But if you have a leak then most probably it is at an evaporator. Please report, I am afraid of that day on my car .... but almost for sure it will come.

Just curious but what temp should the evaporator be normally - especially after new refrigerant has been added? I re-ran the sensor test today and noted the following values:

1. In car temp: 34
2. Outside temp: 19
3. Heater core temp left: 59
4. Heater core temp right: 50
5. Evaporator temp: 19
6. ECT sensor: 73
7. Refrigerant pressure in bar: 7
8. Refrigerant temp:37

During test car was stationary while engine was running.
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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evaporator temp (WITH AC ON!!!!!): between 2 and 5 °C as I can remember, but definitely not more than 6°C (I am 99% sure that 7°C means non-normal situation).

In item 8. you stated refrigerant temperature, but as I know this ought to be blower control voltage (you already have evaporator temperature in item 5).
 

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Green S Class s280 w140
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Discussion Starter #13
mmm... is there any other way I can find out if the evaporator isnt working properly?
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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Look, if we think logically, then we do not know why the refrigerant pressure is so low. Of course evaporator leak is possible but there are also another possibilities (leaks in hoses, etc.). I think the colored refrigerant is the only way to find the leak. If I were you I would take the car to the expert for AC and wait for his diagnosis. Most probably you will have to drive the car for a while to get sufficient amount of leak (color) on the critical point(s). The leaks are visible under appropriate light.
 

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Leaking refrigerant tends to smell like a wet dog, so use you nose. :)

And just for your reference, here's what my evaporator temp does. With both sides set to 72 deg F (22 deg C), the evap temp would vary between 37-41 deg F (3-5 deg C) as the compressor cycled on and off.
 

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Don't workshops usually pump some kind of colored gas into the system to find leaks or is that something else?

I am also based in Dunedin who is the local mechanic that you are using?
 

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Green S Class s280 w140
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Discussion Starter #17
yes they normally put fluorescent dye with the gas. I took the car to a local auto electrician - Harrex, Downing and Little in McBride Street. Total cost was a modest $120. Aircon is fine now with plenty of cold air coming thru. But if there is still a leak there will be deposit from the dye to indicate the hole(s).
 

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2003 Mercedes S320 CDi (W220)
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Hi,
How is the aircon doing nearly a year on?

Shane
 

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Green S Class s280 w140
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Discussion Starter #19
aircon needs another service i think. EC light is OK but aircon i not able to deliver enough cold air when the weather is hot
 
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