Cold AC for 3-5 minutes then gets warm

[Larry12]

My 1998 E300 blows cold 40 degrees F for about 3-5 minutes and then the compressor shuts off.
I can turn the key off and remove it for a minute and then restart the engine and the AC runs fine for another 3-5 minutes.
Low pressure side 100 PSI and High pressure side is 260 PSI.
Both AC radiator fans also start and stop with the compressor.

Sounds to me like electronics under the dash some where.

Where are they and how do I find them and which sensor should I change first? should be 2 sensors or am I off the mark?
I see that Autohauz has both sensors for about $100.

Any suggestions will be appreciated.

Larry12
1998 E300
146,000 miles
1987 300D
250,000 miles

[Larry12]

Any AC help out their?

[tangofox007]

The evaporator temp sensor would be high on the list of probable culprits. Its function is to prevent the evaporator from freezing. When the sensor malfunctions, it trips at a too-high temperature and disengages the compressor clutch.

On earlier models, you can eliminate the sensor for test purposes by jumpering the switch. That would probably work on a '98.

[Matt L]

You cannot jumper the sensor on the W210, but you can put the climate-control pushbutton unit in current sensor mode and see what it reads for the evaporator temperature. With the car cold, it should read the same as the other temperatures. It will be quite apparent that the reading is wrong if it is bad.

[Larry12]

How do I do that? Maybe a step by step for the not to up on what you are saying Matt.

Larry12

[pimpernell]

Originally Posted by Larry12

How do I do that? Maybe a step by step for the not to up on what you are saying Matt.

Larry12

With ignition in on position, turn climate controls on, then press and hold REST for 5 or so seconds, or until you see an 01 flash then another number will flash (inside temp), then back to one, use the arrow up (defrost) and arrow down (feet) to scroll up and down through the codes.

1. In-car termperature sensor (with aspirator blower)
2. Outside temperature sensor
3. Heater core temperature sensor
5. Evaporator temperature sensor
6. ECT sensor (Coolant temp.), e.g. 12*5 = 125C
7. Refrigerant pressure in bar, e.g. 12*8 = 12.8 bar
8. Blower control voltage, e.g. 16*5 = 1.65 volts
9. Software status of A/C pushbutton control module
15. Selected in-car temperature
20. Version code
21. Engine Speed (RPM), e.g. 6*0 = 600 rpm
22. Terminal 58d (Bat. Volt.), e.g. 99.0 = 99% of voltage
23. Vehicle speed (Kilometers Per Hour)
50. Not used – 00
51. Number of current slip recognition (poly-V-belt)
52. Number of stored slip recognitions (poly-V-belt)

[Matt L]

That's for a different model, Pimpernell.

The REST key is correct, holding it down with the key in position 2 will bring up the current-sensor mode. You will see the left and right temperature displays change to the sensor number 1 on the left, and the value on the right. The AUTO keys on both sides go through the codes.

#5 is still the evaporator temperature sensor (but some of the others above do not apply to the W210). Be sure to note the values of #1-4 as well, so you know if you are reading in F or C. Some read in F, some in C, and it is unrelated to the scale used to normally set the temperatures.

[redassag00]

Have you checked the compressor clutch gap?

[oldiesel]

Dont know if it applies to your model,but i had the exact same problem intermittently on my 91 300d 2.5. I changed the serpentine belt because it was looking old and it has never happened since. I would like to be able to say that i figured out that changing the belt would solve the problem but really i never thought of it until sometime later when i realised that my A/C had not quit since i changed the belt,Cheap fix and no problem for about a year now. Don

[Larry12]

OK,Progress! My car reads in C and the readout is 68C and varies between 66 and 68.
Where is this sensor and is 66/68 OK or bad?
What should some of the other reading be?

If I remove this sensor I will probably lose all of the 134a, Right?

Compressor clutch gap is suppose to be? and is measured with a feeler gauge looking straight down 90 degrees from the shaft alongside of the belt grooves?

We are making progress..Thanks for sticking with me on this one as I need the AC to drive from San Diego to San Jose this weekend. And it is 100 degrees here right now.

Larry12

[Matt L]

When the car is cold, the reading at #5 should be very close to ambient. I assume that it is not 65C where you are (after all, you're still alive), leading one to believe that the sending unit is bad.

You do not need to open the refrigerant circuit to change that sensor.

[Larry12]

Very good! Yes, 150 degrees would be a real fast tan condition. Right now it is 90-100 here.

Now how do I locate this item on the car?

I have a dealer within 3 miles so do you have a part number just so that I get the correct item?

How hard is it to get to the evaporator?

Larry12

[Matt L]

The evaporator is very difficult to access. Fortunately, you do not need to access the evaporator to replace the temperature sending unit. I believe that it is located under the dash, on the driver's side.

I've never done one, so hopefully someone who has will post the procedure. If nobody does and I find some time, I'll look it up in the FSM.

[Larry12]

I have the part in my hand (210-830-07-72)

And was able to talk to the service manager and he told be I have to remove the kick paned over the fuel(gas) pedal. And removal of items to get to the evaporator box. It will take about 2 hours,but I will not have to remove and center or dash parts.

Thanks for the help. I will tackle the project in the AM on Thursday.

Larry12

[Larry12]

Job complete!
Thanks!

Took about 1 hour, mainly to remove kick panel from above panels.
I now have 39-41 F cold air from all vents.
Found that the boot around the steering column was mostly gone and letting noise and fumes into cabin. The next project after I replace motor mounts.

Larry12