Our Mercedes A/C system stopped blowing cold air recently, so I purchased an "STP A/C Pro Ultra Synthetic A/C Recharge" with a pressure gauge on the dispenser recommended by a local NAPA auto parts store.  The instructions say that the dispenser needs to be connected to the low pressure port, but I am not sure where the low pressure port is on our 1999 E430.

Is the nipple on the silver pipe in the center of the attached picture of the driver's side of the E430 engine compartment the A/C low pressure port?

Possible A/C low pressure port in driver's side of 1999 Mercedes E430 engine compartment


Thank you for the helpful and quick response! I haven't tried it, because I wanted to be sure, and not inadvertently do any harm.


  I finally got time to try the STP A/C Ultra Synthetic A/C Recharge unit, and it did indeed fit as you said it would, but the needle on the STP A/C Recharge dispenser gauge is always in the red, whether it is connected or not.  Should the needle go back all the way to the left when it is not connected to the low pressure port on the E430 A/C system? 

  Unfortunately I didn't check the dispenser gauge before I attached it to the low pressure port on the E430, so I don't know whether the gauge is broken, or whether it is something else. 

  I am reluctant to "Charge" system from the STP A/C Pro Ultra Synthetic A/C Recharge, out of concern that the system might already be charged, and that further charging will cause damage to the E430 A/C system.  How likely is it that charging the system when the needle is in the red could damage the A/C system?

  One thing I did notice in the E430 is that the EC button on the air conditioning controller is always lit, and the diode won't go off when I push the EC button again. 

  The EC button is for "Economy", and the owner's manual says "The function of this setting corresponds to the automatic mode.  However, because the air conditioning compressor will not engage (fuel savings), it is not possible to air condition in this setting.  Press EC button to activate.  Press EC button once again to return to previous setting. 

  However, the red light on the EC button does not turn off when I press it. 

  So, if the A/C system is stuck in EC mode, can anyone tell me how I can get the E430 A/C system out of EC mode?

  Thanks so much for the help so far in confirming the location of the low pressure port.

It is normal for the pressure to be on red if the compressor is not engaged. But do NOT  charge the system if it is on red. I assume you are trying to charge the system with the engine running. Becasue the engine should be on and running when you try to add freon. 

The problem in your case is that there is a fault code in the AC system which has turned off the whole ac. You may not even need to add freon. 

What happenes is that one sensor in the AC system triggeres a code. AC goes inop. 

All that you need to do is read the AC system codes and clear them. The good news is that you can do it yourself and you don't need any tools. 

Here are instructions which I had to copy from online, as I don't have the steps memorized. :)


It's been a while I had to do this on a W210.

Once you try this, your AC may start working without needed any charging. 

READING FAULT DIAGNOSIS: Ignition in position 1 Set Left Temp to LO Set Right Temp to HI Within twenty seconds simultaneously press the rest and EC for more than 5 seconds The screen will flash "dl R" Now press the right Auto button one at a time until all faults are displayed and recorded All faults must be read out before they can be cleared. To clear all faults press both auto buttons for more that 2 seconds and a "d" will be displayed on the left and "FF" is displayed on the right


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