It looks like something has finally broke on this car I can't fix. While on a 200 mile road trip on Sunday, I noticed the AC wasnt working very well if at all. Car is a 2010 E350 with about 75K miles on it. I hooked up my set of AC gauges on it and it shows about 65 on the low side and 120 on the high side. Cant feel any chill on the lines at all, looks like the compressor is turning ok. There is freon in the system, esp in the high side, I got a blast of it when I snapped the quick connects back onto the mounts on the gauge.



I'm not that well versed in AC repairs and even if I were, I dont have the tools to tear into this. I welcome any thoughts on what it might be or what some typical ac repairs are costing these days. Dealer I bought it from can't take it till next week and wont promise a loaner. There is an Indy in Norfolk that I can drop it off at, I may do that instead.

FYI the AC on those cars operates on at least 9 sensors, while you check only 2 of the parameters.
If you do a forum search - you will find tens if not thousands of topics how to troubleshoot the system.
You will need aprotiate scanner to start with.

Just an FYI. The AC on my 2011 E550 died once. I took it to the dealership and the fix was à software upgrade covered under warranty. If I had tried to fix this myself I would never had figured it out. Not saying this is you issue, but sharing my experience.

According to my neighbor who knows way more about AC than I do, the system is low on freon. So most likely it has some sort of leak. He says there is not enough of a pressure differential between the high and low sides for it to cool.

MB stop using Freon over 20 years ago. So much for good knowledge.

How about R134a? Really? Did that make you feel smart?

If low then there is leakor compressor not cycling enough which with all the computer gizmos today could be any of a number of sensors.

And if you overfill that can do serious compressor damage.

best bet take it to a dealership and ask them to check AC....
Tell them you went on long trip and it just not seemed to be cold enough....

then you can see what they come back with.

The cost of stealer reading the sensors will pay for your own scanner.
To each of his own.

There is another thread with a guy with xentry scanner and that one is not finding codes for the trouble. What scanner do you really recommend to purchase that would magically tell what the problems with A/C system are if xentry cannot do it?

Right now you have several scanners in $150 range, that will read most of MB systems.
I ended up with MaxiEcu and iCarsoft MBII.
Both of them will read AC sensors and there is no magic behind it.

Sold in O'Reilly's today.

Been on this issue on three threads lately. Based on your gauge readings your low side pressure is way too high and the high side pressure is too low. Mine are 32-35 psi on low side and 200-220 psi on high side.

This basically can mean two things. Either your compressor quit working (though you say it is turning fine) due to internal problems or the expansion valve is too much open and does not restrict the flow enough to create sufficient pressure on high side to maintain liquid form of the refrigerant. This prevents the 'liquid-to-gas" expansion that generates the cooling effect.

I don't know what kind of expansion valve MB uses in these systems. Is the opening perhaps electronically controlled or is it set orifice...?

Low pressure on high side means there is no restriction in lines.

In my car when I shut it off the high side and low side pressures do not equalize making me think the expansion valve closes when engine is off. How do your pressures behave when engine is off? If the expansion valve closes but the pressures equalize then it means the compressor does not hold pressure, i.e. it is bad. But, again, if the expansion valve is open too much and does not close it also will allow pressures to equalize.

It is either the compressor or the expansion valve by my guess...

The above would apply to older AC system, who used on/off switch to cycle compressor.
For over 20 years MB is installing variable output compressor, who have variable pressure, so not knowing other factors, you can't draw any conclusion from pressure... unless system is empty.
Funny as O'Reilly's sells r134 as freon, but being technical guy, I pay attention to those things and there are thousands of such misconception.
Another typical misconception is calling propane/refrigerant cylinders a tank. Tank is something welded or bolted permanently.

Hi all,

Stupid question.. when you say "AC wasn't working very well" did you mean that it wasn't cooling? The AC in my 2011 was not coping with 30 degree C (86 f) days last summer and I felt the unit wasn't pushing enough cold air into the cabin. I replaced the cabin filter and airflow was restored so the rest of summer was a comfortable 19 degree C (66 f).

Based on your gauges and information I would think the valve in your compressor has lost its ability to seal the low and high sides. The compressor still turns, but because it is not able to isolate the low from the high side there is no 'compression' and therefore no cooling. I agree that the low is too high and the high is too low.

Dropped the car off yesterday at the dealer. Driving in, I actually felt some cool air coming out. At first they were going to do a purge and refill and then send me home with it. About 2 hours in, they told me that they found that the compressor was bad. So now we're looking around 1800 with all parts and labor. Ouch. Went home with an E300 loaner, should be ready today.