Mike_Shaw

I'm relatively new to the forum and I'm seeking A/C help. The left side blows cold/right side blows warm. I've read the threads here and done the diagnostic test and here are my actual values:

1. 31
2. 28
3. 31
4. 30
5. 42
6. 81
7. 06 (at idle; last week I was reading 13/14 bars)
8. 32
10. 2.7
11. E
12. 4.2
20. 0.0
21. 07
22. 0.0
23. 00
24. 13.3
40. 71
41. 34

I believe I have a bad evaporator tempature control sensor. I have a new one but can't findwhere it is to replace it.

From the above, do you think it is my evaporator temparture control senor? If so, where you I locate it to replace it?

Thanks for any thoughts/replies.

lexrex

Mike,

Welcome to the forum.

Have you checked the climate control codes too? (Instructions for pulling codes are the end of this post.) Fault codes stored in the computer will help solve this problem.

I like to start with the simple things first. You're sure that your EC light is turned off and the temperatures for both sides are set to something fairly low?

Your evaporator temp sensor (#5) is a likely culprit, since it's showing 10 degrees Celsius warmer than the outside air. It's basically impossible for that to happen if your blower fan is turned on. At the time you checked the values, it was at 42 (107 F). That's within the valid range of temperatures that Mercedes expects the system to encounter. Even if the sensor is bad, its value isn't far enough out of spec to trigger a code.

If the problem really is your evaporator temp sensor, you will get cold air for the first 10 minutes after your ignition is switched on. After 10 minutes, the compressor shuts off to protect itself if the evaporator doesn't cool down.

The evaporator temp sensor is located in the side of the evaporator case inside the dash behind the center vents. I believe it is accessed by pulling out the glovebox, but I am not certain. It could be on the other side.

Are you sure you're not imagining that the left side blows cold? Your left & right side temps (#3 & #4) suggest otherwise. The sensors say both sides are nearly the same temp.

You note that your pressure (#7) seems lower than it used to be. Even in a properly functioning A/C system, this number can be all over the place. The job of the A/C compressor is to increase refrigerant pressure to a point high enough that the refrigerant temperature exceeds the temperature of the outside air. Your refrigerant temp (#8) is 4 degrees warmer than outside air (#2). A 4 degree difference is appropriate when the cabin is cooled down and the load on the system is comparatively low. But I would expect both #7 & #8 to be much higher (about 15 bar) when the compressor's running at maximum capacity in such hot conditions. If your evaporator temp sensor is bad, then your compressor will shut down after 10 minutes, and the refrigerant temps & pressures will drop.

That being said, it's possible you are low on refrigerant, but not low enough to trigger a "refrigerant low" fault code. Did you notice any change in the sound of the A/C? Often you'll hear the evaporator expansion valve behind "hissing" loudly through the center vents when you're low on refrigerant. Low refrigerant is often accompanied by the left/driver's center vent blowing warm air compared to the right/passenger center vent.

Hope this helps.

Here are the instructions for pulling the A/C codes I mentioned earlier:

• Set left temp to HI and right temp to LO
• Within 20 seconds press REST and EC simultaneously for more than 5 seconds until the recirculate button flashes and the display indicates "di R"
• Press the AUTO button to cycle through the codes (like you did earlier with the sensor values)
• The letter E (for error) is displayed on the left side and the specific fault code number is shown on the left