Depending on brand and model. Each brand and model has a specific issue that appears more frequently. For example, some of the LG non inverter model and Toshiba inverter. Aircon has sensor receiver issue. Mitsubishi starmex inverter has valve related issue from time to time. Older Midea inverter Aircon has thermistor and PCB issue for its condenser unit. For Fujitsu inverter Aircon it is thermistor related issue.