E350 a/c problems
 

Hi, first post here.
I just got done changing the compressor on a 2008 e350
I evacuated the system, tried to add freon and to my surprise it doesn't take any. The a/c light flashes red 5 times.

My question would be where to locate the low pressure switch, would anyone know? I'm about to do the same job to my slk so I really need to figure this out

With vac on the system with the a/c off I have done a wet charge on other a/c systems. The way I would do it would be to turn can upside down and open it the liquid Freon will go into the vacuum and do a precharge. Then let it sit for about 30 minutes to equalize. This should add enough charge for the compressor to run and cycle, then you should be able to add Freon.

It would be better to know the total amount of Freon needed and have a charge cylinder where you can put the full charge, then with the vac still in fill the full charge. Most people don't have the charge cylinder so use a large can of correct freon and wet / liquid charge. ( I would assume during the assembly of the new compressor you added the proper oil charge and dryer if needed.

The wet/liquid charge is how I get the systems I have worked on up and running. IT is very important to do it with engine OFF and DON'T start it after the charge, if you do the liquid will damage the compressor. WAIT about 30 min or longer for the Freon equalize.

Feel free to get other input then you can decide which is best for you.

The question is----Quote--My question would be where to locate the low pressure switch, would anyone know? I'm about to do the same job to my slk so I really need to figure this out---Unquote

You must not be familiar with auto ac systems and specifically MB ac systems, because there is no low pressure switch on an MB ac system!

Regarding the system refrigerant MB uses three sensors to sense and communicate to the AC control system. They are refrigerant pressure and temp sensors. The third is evaporator temp sensor. The location of the pressure and temp sensor is in the dryer.

However they can not be read with the typical handy dandy fault reader. They can be read by MB's diagnostic software DAS Xentry and it is that software that is typically used to diagnose MB ac sensor problems. A good set of gages is also used to corroborate DAS Xentry as you want at least a constant 17 bar on the high side!!

The MB compressor does not use a clutch and has no "cutout" cycle switch that would normally be in the low pressure line. This is why you should vacuum liquid charge the system.