So last year I bought a 2001 mercedes E55 amg and the ac wasn't working correctly. Since that bought I have put in a new compressor, expansion valves, blower motor, and also blower resistor. These were all professionally installed by a German Mechanic. Last summer the ac worked fine and had absolutely no issues. Well this march we had a few hot days and I went to turn on the ac and of course it started blowing hot air. I drove to my mechanic and he tested the ac and saw the Freon was correct level roughly 2.2 pounds. While he vacuumed the Freon out and put back in he said to me to see if the ac had gotten colder which is didn't. He suggestion to me was that I might have to do a clutch on the fan or replace the auxiliary fans that blow on the condenser. I ordered the fan clutch and also the auxiliary dual fans as well as the spools tool to do the fan clutch. While waiting for the parts I was still driving the car on a daily basis and noticed that the ac got ice cold on one of the days that it was 73 degrees out. I also noticed that the value of the Freon on the climate live data was 18 which I believe is 1.8. The normal level that I have seen is between 6-11 on my climate control. After a few miles of driving I noticed that the 18 dropped down to a 6-7 and the ac started to blow hot air. As with all my other cars is usually the opposite when driving faster. The ac usually blows colder air at on higher speeds of driving. So after reading James's post I decided today to put the live date values from my climate control with the heat on and then with the ac on. Below are the valves I got. Also want to add that my heat works fine but I am about to put a new duo-valve in for preemptive maintenance and also it was a suggestion my mechanic. One last thing I have noticed also that the engine temperature is above 80 Celsius its close to 83-84ish no matter the temperature outside. I did notice the ac worked better when the engine temperature was below 80 Celsius on those few days it actually worked. So onto to the climate control live data values

Heat on : Ac on

1-96 1-87
2-73 2-80
3-154 3-114
4-154 4-127
5-93 5-94
6-179 6-184
7-0.5 7-0.8
8-69 8-75
9-3.3 9-40
10-6.0 10-2.7
11-3.6 11-3.4
12-4.3 12-4.3
20-3.2 20-3.2
21-42 21-42
22-00 22-00
23-211 23-211
24-13.3 24-13.1
40-164 40-164
41-91 41-91
42-72 42-72
43-136 43-136


I would like to add I too did not replace the drier but the ac was working fine last year so I nor my mechanic feel that a new drier is needed. any help would be appreciated

 

You've gotta leak
For full troubleshooting you should read the sensors early in the morning before engine start, to check the calibrations, but....
Your refrigerant is almost empty. I would start with adding a can of R134 with dye and dye only.
This way you should be able to trace the leak.

 

 

 

0.5 bars is empty system. Could be bad sensor - verify with a gauge.

 

 

 

Try replacing the evaporator temp sensor.

 

 

 

 

I think the best way to verify an HVAC system is using a manifold to see the pressure in hi and low sides, with the readings you can say if there is a leak, a bad air compressor or bad expansion valve.it is easy to find the information about the pressures and what it means over the internet.

 

Machadosl,

When my mechanic hooked up the gauges to the high port and low port after the system had be vacuumed and refilled the high side was reading 250 and the low side was reading 50.

 

Well, if the ambient temperature you had that day was about 80 and 85F it seems to be normal, have you seen if when you had the engine accelerated the low side dropping and the high side going up fast? If the high side goes up fast and the low side comes down slowly this indicates the expansion valve is going bad because it is dirty or old.

 

machdos,

Last July my mechanic installed a new compressor, drier, expansion valves, o-rings. I also replaced the sun sensor, outside temperature sensor.. I am basically lost...

 

Assuming everything on the HVAC is new I start thinking if there is a problem with the dual heater control valve, maybe it is stucked in open position.
Here is a video showing it: On one of my cars only one side (driver side) was open and because of this, most of the time on my side was hot . I disassembled and cleaned it and everything became fine again.

 

 

 

Looks like it wasn't 0.8 but 8 bars pressure.
Took 19 replies to get proper troubleshooting, but finally we are getting somewhere.
When you had engine overheating at 66F outside, you might have other problems than bad fan clutch, but replace the clutch and recheck the system.