2 years ago I purchased an E350 12 pass with rear aux ac. The ac was ok then, with nothing to write home to momma. I changed the orifice tub (found trash in it) and recharged. Once fully charged (at idle) tha ac blew warm, the pressures where almost equal. (at 1500 rpm)the ac cooled nicly and pressures where normal. I found today a breakdown of the ac parts to get a price on the compressor. I seen that this systom calls for a "system relief valve". Does anyone know if this is a common failure when you have trash in an orific tub?