is what dirty? the filter? No i just replaced it, the coil isnt dirty. this is a strong working ac unit..
Never seen a walk n with an "air filter" on it (which BTW if dirty would not cause high head). But if you meant a liquid line drier, perhaps you have introduced non condensables. Need more info like refrigerant type, ambient temp, is this a hot pull down, box temp, are all condenser fans running, and this filter you just replaced?