I have a 1999 dodge grand caravan ... My rear a/c works ice cold... but the front vents are slightly cold... When I put 134 in it... (using a meter too) I only put in alittle above the green?blue? line THEN THE A/C OR FREON STARTS SHOOTING OUT THIS VALVE ON TOP OF THE COMPRESSOR... THEN MY CAR SLOWLY BLOWS SLIGHTLY COLD OUT THE FRONT VENTS... I BEEN TRYING TO FIGURE THIS OUT FOR A WHILE... CAN SOMEONE HELP ME??

 

You have too much freon in the system, causing the freon to blow out the releaf valve. You may have a plug H-Valve on the front or a bad mode door.