The air-conditioner is not cold when turned on? Saw some ice forming on the indoor/ fan coil unit when in operation? These are some of the symptoms that your air-conditioner is shortage of refrigerant/ gas.
Being an air-conditioner technician has naturally made me to become a crime scene investigator. We sometimes received calls from customer complaining that their air-conditioner smell bad. Usually the bad musty odour will last for the first few minutes when the air-conditioner is just being switch on; the smells will fade away once the compressor of the condensing unit starts running.