Weird blower motor behavior

[NMerenda]

Tonight I had the heat on in my 02 grand marquis with the digital display HVAC controls. Randomly the fan speed started bouncing around so I turned the car off and turned it back on. The problem then reappeared only under moderate-heavy acceleration, before returning to the proper fan speed. Each time this happened the display kept flashing, as is going between off, and the selected vent option (floor). Has anyone else experienced this, and if so what is the remedy?

[tjc78]

Usually this is the blower motor controller. Mine would do it sporadically until it finally went.

[NMerenda]

Is this the same thing as the resistor? Also what is the process to replacing it?

[IPreferDIY]

Last winter, my blower motor cut out on several occasions before finally appearing completely dead. My solution ended up being to clean the contacts on the motor that the brushes ride on. They were practically black. I used WD-40 and brought back some copper color. I haven't had problems ever since. I'm not saying this will work for you, but it's easy enough to do and would be good preventative maintenance if the motor itself is not truly dead.

AFAIK, the controller is a fancier transistor version of the resistors that other cars have. The problem is sometimes cracked solder joints (though not on mine), which ends up being an easy fix. It's located on the plastic part that attaches to the firewall beside the passenger side camshaft/rocker cover. I think the plastic part is called the A/C evaporator core housing. The controller is under the heater hoses. It only has two bolts/screws but is a PITA to get out. I think the best approach is to use a 1/4" drive socket (I think it's 8mm, but 5/16 would work) on a U-joint attached to a long extension. You can put tape around the U-joint if it wobbles around too much. Some people will drain some antifreeze and pull the heater hoses off, but I didn't bother. Getting the electrical connector off might be a bit of a PITA.

[NMerenda]

I checked fuses (all good), then checked power going to blower motor, all speeds are good, so I reconnected and went for a drive. No erratic fan behavior, at least for now. If the problem arises again I will check power going to the controller. Hoping if anything fails it's at least not the switch! Now that I know what to check for it shouldn't be too bad. Only thing that sucks is it's just in time for winter lol!

[IPreferDIY]

It might be a good idea to clean the contacts on the motor in any event. In theory, dirty contacts on the motor could cause problems for the controller. Pulling the motor is a lot easier than pulling the controller.

[NMerenda]

Thanks, I will give that a shot.