The symptoms of a system overcharged with refrigerant include poor to fair cooling, evaporator outlet warm to cool, and poor to no cooling during stop and go traffic but highway driving may be ok. Both the high-side and low-side pressures will be higher than normal. The compressor clutch may frequently cycle on/off as the high pressure switch detects high high-side pressure. Too much air in system may also cause these symptoms. In addition, when the air conditioning system is turned off on a system with air contamination the pressure will drop 30 psig quickly, but then falls gradually until high and low-side pressures equalize.