njinsa

Hello dear Mercedes enthusiasts,

Recently I've spent a good amount of money to fix the air conditioning on a '02 C240 and got a lot of parts replaced, but it's still not working properly.

The compressor and the dehydrator were the first parts that were replaced. It was a local shop (non-dealer) who took care of it. But they could not get the air conditioning to turn on. No power was going to the compressor, they said. They tinkered around for a bit, couldn't figure it out, so they took it to the dealer.

The dealer replaced the temperature/pressure sensor and it still couldn't get cold air out. Then they figured it was the climate control unit from the front console and wanted $500 for it. After I found it online for $200 at a few places, I sad no, I'll take care of it.

But it seems to me that they don't really know what the actual problem is. So even replacing the climate unit may not fix it.

Does anyone here have similar experience or knows how to fix it?

njinsa

To give some more details, I've tried recalibrating it by pressing those two buttons on the left. It does calibrate fine I think, since it stops after about half a minute. It doesn't help though.

I've also taken apart the climate control unit and looked into it. Everything looks fine, no burned electronics or anything. The thermistor was a bit dusty, so I cleaned it out. I've also opened up the overhead control panel. The thermistor there was very dusty and if the dust was conductive, there might have been a different temperature reading. I cleaned it out. The fan is running even when the car is off. Is this normal?

Still no cold air.

Should I just buy the climate control unit and hope that this will solve the problem?

samaritrey

The fan should not run when the car is off this is a known issue that can drain your battery.
Any chance you could borrow one from a friend or something? any 2001-2007 control unit would plug in and should get the ac turned on if that is the issue. That said if that is what the dealer said (even though I don't trust them usually) I would give it a shot as long as you know that the pressure sensor is ok and that the system is fully charged and that the compressor is working correctly.

njinsa

Thanks for the input samaritrey.

Unfortunately I do not know anyone with the same car. I would buy the pushbutton control unit (N22) if that was necessary. But there are a couple of things that make me uncertain. First, in the manual from the temp/pressure sensor, it says that the trouble codes in the N22 module have to be cleared, as can be seen here:



You'd think that the dealer tried this already, but I don't know for sure, I have to call them up.

If I bought the pushbutton control unit and tried to install it myself, there may be another problem. The following page says that I would have to use the DAS to do some version control:

http://bayhas.com/mercedes/203c-coup...trol_temp.html

So it looks like I can't do anything without having the DAS unit, which means that I have to go to the dealership, and probably get charged like $150 for five minutes of work of plugging in the DAS unit and checking/erasing the codes...

Is it possible also that the thermistor with the fan running on the overhead unit is the reason why the AC is not working? Also, how would I fix it? Hopefully I don't have to replace the whole thing as well. Do I have to replace the entire damn AC system to get this thing to run properly?

Moviela

Are there other problems with the car such as windows or mirrors that do not work? Trouble with functions in the MFD (Multi Function Display?) Seats that do not respond to switches? Lighting not working when doors opened or not responding to light switch?

These would indicate a short or open on the CANbus. If the network cannot communicate, the AAC control push buttons could be affected too.

Without hooking up to STAR diagnostics you are just guessing as to what might be wrong.

You can buy the multiplexer and cables in China for about RMB2,000. (US$325) Then you need a laptop and the software.

The dealer charging an hour is not so steep compared with buying your own tools.

WaveyKat

I also have an 02 C240 and the AC is not working blowing Hot air have been looking to purchase the Compressor but damn would hate to replace the compressor and it still doesn't work..

From what I read, once the Car is turned on with the AC Off only the Pulley From the Compressor should Spin And NOT the Clutch "Middle Section of the Pulley"

When my car Is Started the Clutch & Pulley Spins And The AC Is not On.. so I think my compressor is BAD plus it was reading at above 80 psi Pressure I think when I tired Adding Freon..

I heard before that the codes needs to be clear with the DAS STAR systems. I hooked my STAR and only got "Low Freon" Error. I will try messing with in over the weekend and give you an update

njinsa

I've had some issues with closing the windows with the remote key. The sunroof switch would act funny sometimes. But these problems seem to come and go. Another issue is that the right rearview mirror would not come back to the proper place after it moved for reverse. But I turned that function off, so I don't know if it works anymore or not.

I think you are right. It's a good idea to buy that STAR diagnostics software. After looking around, there seems to be a really good deal I stumbled across. It seems almost too good. Is there something I should be aware of before buying the following:

MB Star compact 3 star STAR C3 professional diagnostic scanner

DarthVader2

What you need to do is to troubleshoot the refrigerant system by getting a manifold gauge set and see what your high and low pressure readings are. All the other things can be working but if your pressure readings are way off, you'll never have cold air coming out of your register. Any automotive A/C shop should be able to hook up the gauge and in a few minutes determine if the pressure reading are within spec.

njinsa

Alright, after talking to the dealer, they explained that it is actually the front SAM control module that needs to be replaced, and not the pushbutton control unit.

I'm considering replacing it myself, but I know that I will most likely have to program it. If I purchase the STAR diagnostic system, will I be able to do the programming myself?

Moviela

You would be able to do the version coding required of the front SAM, but are you sure that is the problem? The dealer wants to sell parts, and wanted to sell you a switch unit, now it is the front SAM. You still might have a problem with the CANbus wiring in the car.

CANbus is a serial protocol that broadcasts data to all devices that are part of the listener pool. Each listener has a unique address, and can talk back to the SAM when necessary. Physically it consists of a shielded wire that runs from device to device throughout the car. There are two failure modes of the wire, open where a connection is not made, or shorted where the signal lead is connected to the shield lead because of physical damage to the cable. You can also have a listener with a shorted input. An example might be the passenger door module that is not allowing the mirror to return to normal after reversing. (although this is probably a fault in the mirror wiring or the sensor on the mirror motion assembly.)

A CANbus fault can be seen with STAR DAS, but you really need a tech experienced with network wiring to find the fault or bad actor with CANbus, then to make competent repairs that won't degrade the system.

Using STAR is not that hard after you learn Teutonic speak because of the literal translation from German, but the programming is v e r y s l o w because the technology is 20 years old.

Kwikdog

Don't know if you've tried replacing this yet... but, it might be worth a shot.

I ran into the same thing on my '05 coupe. Very rarely, I would get AC, most of the time it would blow heated air, as in noticeably warmer than ambient. What I found, was that it was a bad Evaperator Core Temp Sensor (inside the cabin, accessable from the drivers side footwell). Mine was reading -23C, causing the HVAC controler to attempt to thaw out the "frozen" core. It was akward to replace, but not hard. And it was all of $60. Hope that helps!

samaritrey

That one does not look like it comes with the software which can be found online but is a pain to get working. The one I bought came with a VM image that works ok (does have some issues) I put the image on my T420S secondary SSD and run it using VMWARE (so I don't have to use a T43p which sadly is now slow even though I have the best one they ever made) The biggest issue was finding a serial adapter that works with the DAS as it really does not like USB to Serial adapters and most express card serial adapters work off of USB to Serial. That said I found one that does and now Star Runs amazing off of a SSD 8GB of ram and an I7 Processor If you need any advice I can help.