Common signs that your aircon needs cleaning include reduced cooling power despite being set to a low temperature, weak airflow from the indoor unit, musty or unpleasant odors when the unit is running, visible dust accumulation on the filter or air vents, and water dripping from the indoor unit caused by a clogged drainage tray or frozen evaporator coils. If your electric bill has increased noticeably without a change in usage habits, a dirty aircon forcing the compressor to work harder could be a contributing factor. Any of these signs is a clear indicator that the unit is due for cleaning, and addressing it promptly prevents the problem from escalating into more serious and costly damage.