One of my units is
Hi, you'll need to double check refrigerant (freon) charge. working for a day or two, could means there's refrigerant (freon) leak, if there's no leak and refrigerant (freon) charge is o/k, check your electrical, you didn't say what make or model is your a/c, check condensing unit (outside) or evaporator (inside) for solenoid valve it's normally located on freon lines inside of evaporator or condensing unit (outside) check for loose electrical connections, if all (3) don't work, could be freon leak, or compressor not working/running. check compressor and capacitor. make sure compressor is working/running. if it's just one that's not working, then it could be electrical problem with that evaporator that's not working, there's a solenoid valve, that controls flow of refrigerant/freon to evaporator, when you set your thermostat to desired temperature, that's the device that controls flow of refrigerant/ freon to evaporator, it could be in evaporator or condensing unit, or on refrigerant lines, double check, with more info,make/model i could be more accurate. also check your thermostat or senser in unit inside/evaporator. good/ luck.