Why doesn't my A/C cool when @idle? on 2005 Mercury Montego

Static pressure is Low 65 High 150
Running is Low 43 High 150
Both cooling fans are running but my system will not cool at an idle. Temp outside was 66 and the temp in car on pass side was 49 at 1500rpm. Cools fine on the Highway.
Could it be my compressor or something else?

Asked by for the 2005 Mercury Montego
Not sure what you mean on your static readings. With system not running stactic pressures should be equal. I'm assuming you are taking that reading at idle. System could be low on charge by a few ounces. Exact charge is critical. May try evacuateing system and then recharge with the proper charge.