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Juan Crespo
Juan Crespo, Tech Trainer
Category: Mercury
Satisfied Customers: 1513
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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Mercury Grand Marquis LS: installed heater control module in

Customer Question

installed heater control module in 2007 mercury grand marquis it worked for two days and quit so I removed and reinstall and it worked for two days and quit so what is worng
Submitted: 8 months ago.
Category: Mercury
Expert:  Juan Crespo replied 8 months ago.
Hi there.Most likely the blower motor is drawing excessive amperage - which will explain why the original heater module went bad.Just to be sure, go ahead and perform the self test indicated below. Then please let me know the results.To enter the self-test, press the OFF and FLOOR buttons simultaneously and then press the AUTOMATIC button within 2 seconds. The display will show a pulse tracer going around the center of the display window. The test may run as long as 30 seconds. Record all DTCs displayed.To exit self-test and retain all intermittent DTCs, push the blue (cooler) button. The control will exit self-test, retain all intermittent diagnostic trouble codes and then turn OFF (display blank).To exit the self-test and clear all DTCs, press the DEFROST button. The vacuum fluorescent display window will show 888 and all function symbols for one second. Then, the EATC control assembly will turn OFF (display blank) and all DTCs will be cleared. Always exit the self-test before powering the system down (system turned OFF). Intermittent DTCs will be deleted after 80 ignition switch ON cycles after the intermittent condition occurs.
Customer: replied 8 months ago.
Ran the tests. The only DTC that was displayed was 888.
Expert:  Juan Crespo replied 8 months ago.
Well, that's a bit of good news as it means that module hasn't been damaged yet.The part of the system that pushes air consists of three main components; the module you just checked, the blower resistor that controls different blower speeds and the blower motor itself.As I said, you just checked the module, so it is OK. Next, check blower resistor operation by making sure blower works on all speeds. If the resistor is also OK, all you have to do is install a new blower motor and that should prevent any future failures of the control module.Best Regards.

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