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Very commonly this is caused by a faulty blend door actuator Perform the self test on the EATC control head. If there are any memory codes still in the system, the system will not function as it should unless the codes are cleared. To enter the self-test, press the OFF and FLOOR buttons simultaneously and then press the AUTOMATIC button within two seconds. The display will show a dashed line in the center of the display window. The test may run as long as 30 seconds. Record all DTCs displayed. To exit self-test and clear all DTCs, press F-Defrost button. The vacuum fluorescent display window will show 888 and all function symbols for one second. Then, the EATC system will turn OFF display blank and all DTCs will be cleared,