Abstract: The disclosure relates to determining condition data indicative of a blockage of a thermal unit of a heat pump system of a vehicle. The heat pump system can further comprise an air supply unit. A corresponding method can comprise receiving, by a controller comprising a processor, model data indicative of an air flow through the thermal unit and the air supply unit, wherein the model data is based on a model of the heat pump system, receiving, by the controller, measured data indicative of the air flow through the thermal unit and the air supply unit, wherein the measured data is measured via an airflow meter of the air supply unit, and determining, by the controller, the condition data based at least on the model data and the measured data.