I have a 2006 Ford Crown Vic P71 and today I got home and shut her off and the blower motor kept running after turning the ignition off/taking the key out. The fan control switch still works (with the key on or off) high-to-low. The car has working AC, I had been running it but the fan stays on with AC both on or off and when the climate control is set to off with the key off.
I checked the relay under the hood and it’s fine, no moisture in the socket that I could see. I pull the relay and the fan shuts off (obviously). The car has never done this before. I disconnected the battery, let it sit for two hours, put the relay back in, connected the battery and the fan came right on without the key in the ignition. Nothing else powers up with the ignition off, as normal.
The car doesn’t have EATC, it’s all manual switches.
For now I just pulled the relay so it doesn’t drain my battery but am trying to figure this out before the cold weather hits. I will wire in a seperate switch and circuit from the fan if I need to but would rather fix it correctly. Not sure where to start looking next, this makes no sense to me as to how the blower motor would still be getting power with the ignition off, nothing else is getting power, per usual.
Your relay has likely welded its contacts closed so the fan runs continuously. Either test the relay to confirm this guess or just replace it. I’ll bet that fixes it.
Without hands on, I’m guessing the blower control module has failed due to age and heat. You may find the connector plug melted and wires touching.
If that is the case then you need to consider replacing the blower motor also. It’s amazing the amount of current a worn blower motor can pull.
Some yeara ago my wife came in one day and said the blower had quit for a few minutes on our Lincoln. I went out to check and found it to be quiet, blowing plenty of air, and no obvious problems.
A check with an ammeter showed the blower was pulling 27 amps on the HIGH setting and that will fry just about anything.
@Mustangman makes a good point about the relay contacts being shorted, that is a possibility. I suspect there is another cause for the issue, especially if your car has a variable speed control for the blower. I think it does. If that is correct that means there is a solid state speed controller in series with the blower motor power. The transistorized module can fail in two ways, either open or shorted. In your case it would be shorted, power is then passed through the module and to the motor. Power is provided to the motor at all times. The module will be connected to the motor and fastened to the air duct for cooling.