Help With '99 C280 A/C Diagnostic Codes
 

I need a little help here with the a/c in my '99 C280 with 120k miles. The unit is not putting out cool air. First I thought it was out of R134a and when I checked it with a pressure gauge, it was reading zero. However, when I tried to put in some R134a, the pressure reached the 25-45 mark even though the can of refrigerant is still almost full!

I took the readings from the dashboard control console and these are the numbers I got with the car having being parked almost 24 hours without being started.

Engine Not Running; Key in position #1.

01 = 79F
02 = 70F
03 = 77F
05 = 122
06 = 75F
07 = 01*4
08 = 69F
09 = 50F
10 = 250
20 = 00
21 = 000
22 = 000
23 = 000
24 = 12.3
40 = 03
41 = 03
42 = 26
43 = 6-C
50 = 50F
51 = 72F
52 = 50F
54 = OFF

Engine Running, Car Was Not Driven After Sitting Parked For Almost 24 Hours. Reading Was Taken Immediately Car Was Started.

01 = 78F
02 = 70F
03 = 75F
05 = 122
06 = 125
07 = 01*4
08 = 69F
09 = 50F
10 = 260
20 = 00
21 = 000
22 = 000
23 = 000
24 = 13.8
40 = 03
41 = 03
42 = 26
43 = 6-C
50 = 75F
51 = 72F
52 = 50F
54 = OFF

From reading other similar posts here on the Forum, it appears that #05 represents my Evaporator Temp Sensor, and it appears that it is running hotter the Core Sensor which I believe is represented by #03 above. Am I correct in this analysis? And if so, what does that all mean and how do I go about fixing this problem. Also, I tried but did not get any error codes, or maybe I didn't do that part correctly?

I would like to get this reapired before the Chicago summer heat gets here and would really appreciate any help given.

Looks like your problem(s) are related to #5 evaporator temp sensor & #7 refrigerant pressure.

Evaporator temp MUST be less than heater core temp!

Refrigerant pressure in BAR should be between 4-8.

M.B.DOC, I am inclined to agree with you regarding the evaporator sensor because I got the high temp reading with the engine not running and the car having sat parked for almost 24 hours! From reading other similar posts here, it appears the sensor is located somewhere under the driver's footwell?

The next obvious question then is, how do I go about replacing the sensor? How much does the sensor generally run? And is it a part I can purchase from the forum parts store?

As for #7 and the refrigerant pressure, could it be because the compressor is not really kicking in due to the high sensor reading? Also, the pressure gauge I used is one of those that you purchase or come with R134a cans in the store. It has both a color and number coded gradient going from 0-200psi and the colors green(Low)/blue(Filled)/yellow(Alert)/red(Warning).

My instinct is to replace the evaporator temp sensor and then go from there. Can I hope for any guidance in replacing the sensor from you or any other forum member? And, thank you for your input thus far.

MB number 210-830-07-72..with a $69 list price...I would think $50-55 would be a fair price.

Pressure is too low & will require a re-charge.

Where can I find the DIY instructions for replacing the evaporator sensor?

Not on WIS, guess MB deems job too simple.

Removal of the drivers under dash panel is required. Located above gas pedal area.

Thanks, M.B.DOC. I also had gone to my local library and checked out the ALLDATA info for this item. The ALLDATA site has a photo of the underside of the driver's side dashboard, but unfortunately, it was not a very sharply focused picture. The ALLDATA photo or site does not have any written word direction for this repair. You have just the photo to guide you. However, once you get your bearing by knowing what you are looking for and where to look, the slightly blurry and not very sharp photo makes a bit more sense. Nonetheless, I now know it is definitely a repair I can handle.

I am going to wait until I get the sensor. I actually found it at a couple of online stores for $36 and $39 plus shipping. I will post a feedback once I have it installed.

M.B.DOC., while I am here, what's your opinion on synthetic R134a? Can it be safely mixed with regular R134a?

I have installed a new evap temp sensor and am now getting the following diagnostic readings:

01 = 98F
02 = 81F
03 = 91F
05 = 91F
06 = 177
07 = 03*.0
08 = 84F
09 = 50F
10 = 495
20 = 00
21 = 060
22 = 000
23 = 000
24 = 13.8
40 = 03
41 = 03
42 = 26
43 = 6-C
50 = 89F
51 = 60F
52 = 50
54 = OFF

From the above readings, it appears that my evap temp sensor reading has improved from what it was before (122), but it still seems to be running high. Please correct me if am wrong, but I believe I read somewhere on this forum that it should be running much lower.

Also, it appears that my a/c compressor is not kicking on because am still not getting cold air from my a/c. The R134a pressure is a little higher than it was before but that may be due to the 5oz or so I was able to pump into the system before the pressure indicator climbed close to the yellow line on my pressure indicator gauge.

My question then is this; why is the compressor not kicking on and what can I do to correct that and get an ON reading from #54 above? Am I getting a wrong R134a pressure (content) reading due to a faulty pressure gauge? And, shouldn't the refrigerant pressure bar be higher than 03*.0 if the canister is really full? M.B.DOC or any other member out there that can , please help!