Why is my A/C High Pressure side values so low?

Question by glennmartin posted 2 months 2 weeks ago in 2003-2009 (W211)

I just bought an A/C Manifold Gauge Set to get an accurate reading of my Air Conditioning System because it is blowing warm air. I was hoping that all I would need to do is recharge the system but I suspect a more difficult repair is at hand.

STATIC READINGS (Engine Warm. Engine Off) External Temp 75F: 

Low Side : 30 psi

High Side: 25 psi 


DYNAMIC READINGS (Engine Running 2000 rpm) External Temp 75F: 

Low Side: 32 psi

High Side: 35 psi


There is a loud rattling noise coming from the engine compartment but I have not determined that it is the A/C Compressor but am pretty sure that its the noise maker since it started making noise about the same time the cooling in the cabin stopped working. 


I do not have an OBD II reader that can get the A/C codes from the system if anyone bothers to ask. 


Thank you in advance for any advice you can give.