A method is provided for testing the performance of a vehicle-mounted heat exchanger and determining whether debris is preventing air from efficiently passing through the heat exchanger. To test performance, after the vehicle is traveling faster than a preset minimum speed, the power to the DC fan motor that is adjacent to the heat exchanger is interrupted and the back EMF of the motor is used to determine fan motor speed. As rotation of the unpowered fan motor is due to the air flowing through the heat exchanger, the rate of fan rotation is used to indicate the relative health of the heat exchanger. If the rotation of the fan motor indicates insufficient air flow, then a notification message (e.g., visual or auditory warning indicator) is transmitted. If the test indicates sufficient air flow, normal operation of the fan motor is re-initiated and power is re-connected to the motor.