Most common for any low to high diff and a blockage issue would have to do with the expansion valve. is this a old r12 system? Is the fan kicking on? I don't think replacing the condenser unless smashed or in some serious state of decay will be the issue. Make sure there is no particles in the system, thus you will have a blockage issue with the expansion valve. Make sure you have a air exchange with the inside and outside high and low. Meaning your air handler must be working 100% if its not switching over inside sending the air over the low side coils it will get lower on the low and higher on the high... also the same effect from the high side can be said,,, if air is not passing over the high side coils aka condenser you will have the same effect. its basically a balanced equation. both have to work with each other... make sure the fan is working 100% and there is nothing interfering with the heat exchange. Ac systems are very simple when it comes down to it. It can only be a few things as which i stated. Also adding a lil oil to the system can not hurt at all. Some comes out when a system leaks or gets a breach. Hope this helps.