Automotive Air Conditioning Information Forum

This is a 1999 Mercedes e300 I've had for decades.
I replaced the condenser, compressor in the past and the AC worked great for about 3 years. This summer I was getting hissing at the center vents and uneven temp air coming out the vents. Now the EC button illuminates automatically and stays on,and if course no cold air.

I went to top up the refrigerant and the gauge on the low pressure side reads filled. But sensor 7 reads 03 bar.

I pulled the error codes and sensor readings below.
Error codes are for the circulation pump and refrigerant temp sensor.

Sensor readings follow:
1: 84
2: 93
3: 107
4:107
5: 82
6: 177
7: 03
8: 120
9.....
10: 1.5
11: 2.3
12: 3.9
20: 3.2
21: 42
22: 00
23: 32
24: 13.3
40: 164
41: 62


In addition to the refrigerant temp sensor being bad, what does it mean that the low side shows full pressure but sensor 7 reads so low? Could it be a restriction in the drier?

Thanks in advance for any and all help.

Whoa!!!
"I went to top up the refrigerant and the gauge on the low pressure side reads filled."

1. what makes you think it needed refrigerant?
2. The low pressure gauge says it is full?? There is no possible way to tell from any pressures if the system has sufficient refrigerant or not. Whomever taught you AC taught you wrong.
3. Are you using a professional type Manifold Gauge Set meaning with red, blue, and yellow hoses with both a hi reading and lo reading gauge?
4. We assume the refrigerant is R134?? Confirm.
5. Not sure what country you are from but giving pressures in bar means you are not USA. So, in this country, in auto parts stores there exists a tempting fancy looking canister with a hose and a low pressure gauge only, and these typically have not only refrigerant, but also any number of undesirable additives such as sealer. Installation of these products are verboten to an AC pro, as this will clog your system and render it useless, while providing you with a reason to now spend a boatload of cash to undo the damage. So, in your country, are these type canisters available and used? Is that what you have done in the past?

We can help you if you can answer the above questions, and provide the following info:
Any mobile AC system is evaluated by a pro by doing all these things:
1. engine RPM 1500-1800
2. using a pro-type gauge set with the 2 gauges as described above, provide us with both the hi side reading and the low side reading.
3. AC should be set to max cool, and max fan.
4. doors should be open (you want a maximum load test)
5. Using a digital thermometer, provide us with the center vent temp
6. provide us with the ambient temp.

With that, we can go from there. The codes you included mean nothing until we get this very basic info

tbirdtbird wrote: ↑Thu Oct 27, 2022 5:29 pm
2. The low pressure gauge says it is full?? There is no possible way to tell from any pressures if the system has sufficient refrigerant or not. Whomever taught you AC taught you wrong.

I was rolling my eyes before I even got to tbirdtbird's post !!!

A friend is a Mercedes mechanic. He says 1) the codes will not do any good at all. 2) In all likelihood you have a vacuum leak, ie the blend doors are vacuum controlled, especially the way you describe the uneven temp at the vents. You could be dealing with re-heating. Easy enough to check. For starters do you get any cold air when the engine first starts up (ie not warm enough yet to cause re-heating), In that era, Mercedes loved using vacuum lines for everything.

We still need the info asked for before in order to check the health of the entire system.