Thank you in advance for any help!
2009 Grand Marquis the A/C controls for heater/vent /defrost/ac/hi-lo speed won't turn off at all. When I press off the display goes blank and the fan blows harder. The best I have been able to do is press vent/defrost and hope the fan is not going to blow fast. Rarely when I do this and try turning down the fan speed wheel it may slow a little or blow at maximum speed. Please, any ideas on what I should look at first?
You need to have some one put a scanner on the vehicle to see if there are any A/C codes stored in the body computer.
If there are any A/C codes stored in memory then they should be repaired first.
Check with your Mercury Dealership to see if the A/C system is under any kind of warranty according to the age and mileage of your vehicle.
You may have a problem with the blower module or the A/C control module. Sometimes there are ways to reset the system because it could electronically lock up causing the malfunction. There are times that the modules may have to be reprogramed to a newer software. Check with the dealership on this, I didn't find any service bulletins on this problem.
Once the scanner is put on the car then the mechanic can give you a better evaluation on the condition of the electrical components of the A/C system.