W210 Air Conditioning System Fault Codes

[JimSmith]

I have been having a persistent problem with the driver's side (left) dash vent, and the footwell vent, arbitrarily deciding to go from a set temperature to full heat. The only way to correct it is to set the automatic control to "Defrost" and endure a few minutes of intense heat, then turn it off and the system goes back to normal. For a while.

So, I dug up the diagnostic/code check procedure, printed it out and ran through it with the engine all warmed up and the air conditioning system in its mode of misbehaving. I got a code "Eb 1 459" which is "Series Interface (K2) connection to instrument cluster (A1)" and another one, which is not listed in the article, "E FF" and then pushing the Auto button again just makes them repeat.

Anyone know what these mean, and what I have to do to fix them? I am about to start my first air conditioning system repair ever and could use some advice or hints. Thanks, Jim

[Gilly]

Jim
Not familiar with the article or the codes being presented with these numbers
The "Serial Interface" code between the ACC and instrument cluster is present on most all of these. The interface isn't used until much later.
One problem I do know of that can cause this is the evap temp sensor. Maybe you can figure out how to monitor that and compare when it's operating fine and when it's in a failed state. Easy to replace.
Gilly

[JimSmith]

Gilly,

Here is the link to the page:

http://continentalimports.com/ser_ic40142.html

In Chart 3, kind of hard to read, it shows that the first code I get - the Eb1459 (spaced out a little differently on the display) - is the K2 to A1 connector. There is no reference to the E FF code.

I forgot to note the system behavior does not depend on having the A/C on. It is presently in the 40's Fahrenheit here, so I have the unit set to "economy" and get the same symptoms and the same responses - ok, then all hot on one side, turn the windshield defrost mode on, cook for a while, and then turn it off (push the button on the ACC console) and all is ok for a few minutes to hours. The exact same behavior when the compressor is on, or if the system is in "Auto" mode or I have manually set the fan speed and selected an air distribution setting.

That link suggests I can get the evaporator temperature reading by pressing a sequence of buttons. I will give that a try and see what, if any difference there is when it is ok and when it is acting up. Thanks, Jim

[JimSmith]

Gilly, I did not really understand what you meant by:

"The "Serial Interface" code between the ACC and instrument cluster is present on most all of these. The interface isn't used until much later."

Did you mean this code is not a sign of a fault and the serial interface is not on my car, on purpose? Thanks, Jim

[Gilly]

"on purpose" if you want to call it that. The easy thing for me to say is "ignore that code, they ALL have that code, it's not a problem". There is no interface, even thought he acc control unit could accept it, and faults itself for not having received it.
Gilly

[JimSmith]

Thanks, Gilly. I will take a shot at reading the evaporator temperature in both operating modes today. Jim

[JimSmith]

Gilly,

I recorded the following information using the procedure outlined in the linked site:

Key for Measured Attribute______11/19 OK__11/20 Malfunctioning__11/20 OK
1.In-car air temperature sensor:____73 _______76_________________80
2.Outside air temperature:_________87________48_________________48
3.Left heater core temperature:____98_______130_________________69
4.Right heater core temperature:__100_________87________________71
5.Evaporator temperature sensor:___39_________39________________40
6.ECT sensor (DFI, IFI):__________177________170_______________168
7.Refrigerant Pressure in bar:_______15_________04________________04
8.Refrigerant Temp Sensor (F):_____125 ________57_______________51
9.Not Used (but has numbers?):_____40_________51_______________51
10.Blower control voltage:___________6.0________6.0_______________6.0
11.Emissions Sensor (voltage):_______2.6________2.2 _______________2.2
12.Sun sensor (voltage):____________4.3________4.3________________4.3
20.Aux. fan control current (amps):__10.3________3.2________________3.2
21.Engine speed (x100=rpm):________4.2_______69_________________60
22.Vehicle speed (km/h):____________0.0_______67_________________37
23.Terminal 58d (%Battery Volts):__211________211________________211
24.Battery Voltage:_______________12.8_______12.9________________12.9
40.Software Status:_____________164________164________________164
41.Hardware Status:______________32_________32_________________32
42.Unlisted/Unknown:_____________72_________72_________________72
43.Unlisted/Unknown:____________152________152________________152


It should be noted the car was idling in the first set of recorded data, after being fully warmed up and driving for about 25 miles on the highway. The air conditioner compressor was shut off, with the system set in "Economy" mode and the system was operating more or less as it should, with about equal temperature (cool) air coming from all four dash vents. The outside air temperature reading is way off because, in all likelihood, the engine operating had warmed the air under the car, giving a false high reading for the sensor under the front bumper.

The second set of readings took place on the highway with the air conditioning compressor on (by pushing the "Economy" button to turn it and the little red light off). After the system was operating normally for a while (more than 5 minutes), the system switched itself into its autonomous mode. In this mode the system operates with very hot air spewing out the driver's side dash board vent and footwell while the same vents on the passenger side were cool. Even the driver's side center outlet was warm while the adjacent passenger side center outlet was cool. The temperature settings were set in "Automatic" and "72" on both sides for the duration of this event, including while the readings were taken. I question a number of the identifyers in the chart referenced on the previously linked site, which I have copied over in the table above. Items like the rpm and the vehicle speed just don't make sense so I imagine there is a newer key to figuring these things out.

After recording the data for the condition noted in the second column above, I put the unit in "Defrost" mode for about 5 minutes, cooking the inside of the car. Then I switched the "Defrost" mode off by pressing the push button and the system recovered, the compressor came on and the cabin cooled pretty quickly. The third set of data was recorded while in this recovered condition while driving initially on the highway and then the last few miles on a side road.

When I look at the data the most obvious thing is that when the system is in autonomous mode, the heater core on the driver's side is pretty hot and the one on the passenger side is not. So something is telling the valve to open or the pump to pump. Any ideas? The rest of the stuff looks pretty normal to me. Thanks, Jim

[JimSmith]

Gilly,

I am hoping you see this and check out the data. I am not sure where to begin with this one, as I live in fear of meddling with the unique to MB electronics on this car. Any ideas? Thanks, Jim

[Gilly]

I took care of the problem over at Open Discussion, thanks.

The reading you gave me has me thinking this"
In the failed state, you get hot air on the left side (the fact that it's split evenly even at the center dash vents is OK, it will do that if you set one side hotter than the other.
If you have the temp set the same, but one side is hotter than the other, I would first begin to think along the lines of a new "duovalve" (heater valve with seperate L/R function, as opposed to the early "mono water valve").
The readings seem to hold up that the system may be actually operating fine, as it is reporting a left heater core temp much hotter than the right. I think the valve is pretty expensive, but unless the left side of the duovalve is being incorrectly regulated, I don't know what else to say. I believe the SDS can try commanding the valves open or closed, or you could pinch off the hose for the left core when the system is malfunctioning and see if the air cools down.
Gilly

[stevebfl]

I have a good customer with exactly the same situation. I agree with Gilly on the likelyhood of the duovalve, but haven't been able to catach the problem even though I have driven the car at least 40 miles.

I drove the car while monitoring the control signal to that side of the duovalve. With no problem I saw no problem.

The only thing the your data tells me is that the heater valve did go open, everthing else is fine. Whether it responded to a command or just did it is the last piece of the puzzle. On my car there the SDS did not show the command nor give capability to initiate the command.

[Gilly]

What I'm not sure of (and maybe Steve is) is if the duovalve operation is similar to a mono water valve. If it is, you can get it in a failed state and find out if there is voltage to the control wires for the left side, you'd need to research which wires control this for the left or right.
If the scheme is the same as a mono valve, there should be NO voltage present, which represents valve ON, this would indicate a CONTROL problem, or if there IS voltage there, it represents valve CLOSED, which means the duovalve is the fault.
Gilly

[benzfan]

This is the exact problem I posted a question about the other day for my 96 C280 (no replies). Only on the 202, there is only a single readout for heater core temperature, as I do not have the dual zone head unit. I will be at the dealer in the morning to have it checked out. I can only think it's a duo-valve problem, but I'll let you know what they tell me.

[benzfan]

And the verdict is - duo-valve.

[reelphun]

Greetings,

I bought my 97 C280 sport 12 months ago. About four months after I purchased it the A/C output temp. stated to get warmer. I took it in to an A/C shop and they put a half a pound of refrigerent in it and it was cold again. They could not find any leaks. Six months after that the A/C started to get warmer again. I added a can of 134 refrigerent myself and it was ice cold again. Prior to that I noticed that when I accelerated the air volume comming from the vents would slow down. Last week It stopped blowing cold all together. I looks like the clutch is not engaging.

I went to the continental Imports site (http://continentalimports.com/ser_ic40142.html) about using the in dash A/C control to find fault codes. My A/C controler is slightly different than than the one in the article, it doesn't have the red/blue hot cold buttons on both sides. Is there a way to find the fault codes on my C280 A/C system.

Reelphun

[Norman123]

Jim,

Thanks for the link to Continentalimports.com, great article. I tried it on my 1996 E320 and was able to read all the codes.

Thanks