Josephabdo

Hello Guys,

I'm a new mercedes owner and I don't know if this thread has already been opened (did some searching but couldn't find a similar one).
I drive a 2010 E350 coupe, when I start the AC for the first time in the morning, the blown air is not cool at all, (as if the compressor did not start)
However with some throttle, it works just fine and continues to work until the car is off for a few hours, (I try it again after 9 hrs work) then the same issue happens again.
I did a gas vacuum and reinstalled gas, and changed some kind of a valve that is located on the compressor but the problem was not solved.

My local workshop suggested to replace the compressor but I would really appreciate ur advise before doing anything.

Thank you.

Plutoe

You want to call around and have them put a set of gauges on the car to make sure the compressor is working properly, however the best alternative is find a garage that has the DAS Xentry diagnostic tool----they will find the problem in five minutes!!


PS: Your car does not have any AC selftest!!

Josephabdo

Thank you Plutoe,

Could you please explain what kind of gauges?

Unfortunately it will be a little difficult to find workshops with advanced tools where I live (Lebanon), so I was kinda hoping that someone in the forum had experienced the same issue and could share this experience.

- Is it possible that a malfunctioning compressor doesn't start immediately but with throttles it starts and works normally until the car is parked for several hours?
- Could it be a normal behavior and maybe it has some kind of delay?

I'm not even sure if the compressor is starting or not, but I am sure that it doesn't blow cool air until the rpm is above 2000 for a few seconds.

P.S.: I am in a wheelchair so it's a little hard for me to diagnose the problem myself, but honestly I don't really trust the mechanics we have here and I know you guys are more expert than most of them.

Thank you.

Plutoe

I can appreciate your concerns, however, automotive diagnostics has not advanced to the point of telepathy. Therefore all over the world we will still have to rely on trained mechanics who know the car,who are at the car and have the basic tools to repair the specific model of car---or individuals with the skills and tools.

Based upon your post you won't be able to diagnose and\or fix the car yourself therefore you will have to find someone who can or sell the car.

I don't believe you about Lebanon--there are many factory trained mechanics in your country--maybe you have to look harder.

Regarding gauges---simply Google "AC gauges" there are millions of threads on the topic.

Regarding the design and function of the MB AC compressor system---simply Google--there are thousands of threads on the topic that you can learn from!!

Josephabdo

I don't understand what you are so upset about.
I know that a well trained mechanic with the good tools can diagnose and repair the problem and that I need to find one, and I know that I can do researches on google.
I was asking if someone had ever experienced the same problem and has any useful advice other than google and going to a mechanic of course.
I appreciate your time but if you can't answer my questions then just don't.

mo11

I'm not an expert but, what i've noticed is if the outside temp (displayed in the dash) is a "comfortable" 70-73*f, and the thermostat setting on the a/c is above 68*f or higher than the outside temp, the compressor doesn't run. Adjust the thermostat to 67*f or lower and cool air starts blowing. Idk if this a factory "intelligent" setting. I guess it thinks that cool air isn't needed yet.

Josephabdo

Thank you mo11 for your reply,

Actually I tested what you suggested and I set the temperature to lo (the minimum) and still faced the same issue and on very hot days 30* + Celsius.

Late

um im confused. Doesn't every car take a little to get the ac blowing cold? i mean i've never owned a car where the ac temperatures are immediately cold as soon as i start the car on a blistering hot summer day?

How long does it take for the air to start blowing cold?

Josephabdo

you are right, the air cannot be cold immediately, but in my case u can easily notice that it's only regular air, As if only the ventilation is on and
It stays that way until you step on the gas fir 2-5 seconds (once I waited for 10 minutes)

Late

hmm okay so building revs causes the air to blow cold. The only item in the ac system that would be affected by the engine revving is the compressor since it is connected by the serpentine belt.

Next time you start up your car turn the ac on full blast and without touching the gas inspect to see if the compressor pulley is spinning with the clutch engaged ( the middle part of the pulley needs to be spinning not just the outside of the pulley where the belt is).
Its possible that the additional speed of the the serpentine belt engages the clutch in the compressor? or the clutch is worn out and it is slipping until the pulley spins a little faster? if you throw a camera on the compressor and record it from engine startup you should see the center of the pulley "Suck" into the compressor about 1mm or so when the clutch engages

We know that the AC works just not at startup... so i dont think you have a problem with the system charge. This does sound like a compressor problem to me.

Josephabdo

Thank you Late,
I'll try to test it the way you explained ASAP.
I don't know how this can help but since I got the car (About 4 months ago) I used to turn of the AC before turning of the car, however during the past 3 days, I kept the AC on and I noticed that it starts with the car every time, I'm gonna test it the same way for few for more days to confirm that it's not a just coincidence since the problem does not occur every time. Maybe it's a dummy question but do you think that when the car starts there's actually more spinning or maybe more power given and that's why the compressor starts?

Late

yea exactly, the belt will spin faster with more engine revs and when you crank the engine at startup the revs will most likely jump a couple hundred rpms over your idle rev speed. So if your AC is sending the signal to activate the clutch of the compressor, at startup, the extra cranking RPMS would cause it to engage. I believe it is just a 12v switch that tells the coil inside the pulley to engage the clutch so maybe at idle there just isn't enough power in the electrical system to tell the switch to engage.

During startup you will also have more electrical voltage ( i believe about 14.1 volts) before it goes back down to the running 12v. Basically the coil acts like a magnet that sucks the clutch into the pulley then it grabs the pulley and remains activated. So if it works at startup and when you are giving it revs i would actually lean toward it being an electrical issue where idle isnt producing enough power to turn the coil on