Air filters are critical to vehicle Heating, Ventilation, and Air Conditioning (HVAC) systems, ensuring cabin air quality by trapping dust particles that accumulate over time. However, conventional clogging diagnostics—such as physics-based simulations, empirical models or manual inspection—are often too complex or impractical for in-vehicle deployment. To address this, we present a simple and practical diagnostic approach for real-time detection of cabin filter clogging by continuously monitoring the pressure drop across the filter–evaporator assembly at five blower speed settings. Baseline pressure drop values were established for a clean filter in a production-spec Passenger car and the clogged filter threshold was defined by a 10% reduction in airflow. This corresponded to calibrated pressure drop values of 83, 108, 169, 212 and 256 Pa for blower speeds 1 to 5, respectively. These thresholds were programmed into the vehicle’s climate control ECU. During operation, when the measured pressure drop exceeds the threshold for any blower speed, an electronic alert prompts filter replacement. Experimental validation confirmed reliable detection and timely alerts for filter clogging at every blower speed setting evaluated and in all five tested vehicle units. This low-cost, easily integrated solution enables condition-based maintenance and improved cabin air quality experience and can be readily adapted to a range of automobile models without significant hardware or system changes.