xsever

Hello All,

One year ago, my AC stopped working. It would suddenly stop blowing cold air when driving especially when stopped in traffic.

It was diagnosed by my indy #1 to have a bad compressor, and a new OEM compressor was installed along with a full system flush and all. The compressor installed is a Denso 7SEU17C 03E11560 Made in Japan with the MB logo on its sticker.

The AC worked perfectly after that until about a month ago where the AC is not cooling very well and sometimes, when stuck in traffic, cold air stops coming out. I am using a multimeter which is capable of temperature measurement and for example yesterday during the day, the outside temperature was 35C (95F) and the AC was blowing 14C-16C (57F-61F). When I got stuck in traffic, the AC air temperature increased to 20C (68F) and I could smell that humidity smell.

The night before, it was much cooler obviously, the AC was blowing air at 8-12C (46-53F), but when I hit traffic, the same happened where the air temperature increased to 20C (68F) and I could smell that humidity smell.

My indy #2 is saying that these symptoms point towards a faulty compressor, but I don't want to just throw parts at the car. He is suggesting I replace the compressor with the older generation one which he says is more reliable as he is doing that with many cars that come to him with this similar problem and the results have been satisfactory. That compressor is the DENSO 7SBU16C which is fitted on the W208 and W210.

I do have access to a STAR but not when driving and when the problem occurs, but I am going to do a scan tonight and see what comes up.

Any clues/tips from previous experiences you guys have?

My Car is a 2005 CLK 320 European-spec and I have the basic AC system (without the sun sensor and dual zones).

Rudeney

Whatever they do, when the system is opened,make sure that the drier and the expansion valve are also replaced.

xsever

Hooking up the car on STAR and checking for fault codes, we found a fault code pertaining to component B12 AC Refrigerant Pressure and Temperature Switch. We replaced the part with a new updated one (ending with 04 72 vs the old 03 72) and refilled with R134a.

Unfortunately the problem remained. We then replaced the valve that's connected to the compressor. Things worked for a day, then the problem came back and there are no fault codes on STAR after the first one.

We then suspected that it might be a Front SAM problem so we swapped SAMs to see if that solves anything and no luck neither.

The indy is now saying that we are left with changing the compressor and the condenser and making sure the system is fully clean (at a cost of $800). He is worried that when the compressor was replaced a year ago, debris from inside the system were not cleaned properly and that is what caused the compressor to fail again.

Amy thoughts on this from the community?

Rudeney

Does the compressor engage? If it is, and it's not cooling, then assuming the system is properly charged, I'd look at the expansion valve.

xsever

Yes the compressor is always engaged: both when it's blowing cold or not. When things are working well, the High Pressure (HP) reads 15 bar and the Low Pressure (LP) reads 2.1 bar.

When I lose cold air, HP drops to 10 bar and LP increases to 6 bar.

The indy is saying that with these readings, there is no problem with the expansion valve. The symptoms which indicate a bad expansion valve, according to him, is when one of the values deviates from the normal reading but not both.

We are heading towards changing the compressor tomorrow or the day after. He said he has treated this same problem many times with other customers and it's always the compressor with these symptoms.

Something interesting he has been doing however is replacing the compressor with the older-generation one just like I said in my first post. He swears by it and will guarantee such system for a year.

Rudeney

Any significant differential in the pressure and suction lines will indicate that the compressor is working. I would agree that when it starts varying like this that it might be the compressor. What concerned me was the comment about your mechanic trying to bleed the system due to "high pressure".

xsever

Work so far revealed very dirty lines with black residue and a non-OEM expansion valve. We are going to flush and clean the entire system before playing it safe and replacing the following:

1. Compressor (installing the old generation compressor)
2. Condenser/Radiator
3. Expansion Valve

Will report with updates.

xsever

Older-generation DENSO SB16C compressor installed along with a new condenser and expansion valve and the AC system has been performing tremendously even in high temperatures and heavy traffic.

Rudeney

Good to hear!