I have a 2000 Grand Marquis LS and sometimes the EATC works and sometimes I just hear a loud blowing noise in the dash while just a faint stream of air comes through the vents as if there is something blocking the airflow. Also, I have heard a fairly loud bumping noise under the hood on the passenger side of the car. This started a couple of weeks ago and at one point nothing would work at all so I checked the two fuses and they were OK. It still did not work until later that day I tried it again and it did work. But occasionally it will just make the loud blowing noise. Thanks for any help.
Sometimes mice get inside and make a nest causing a blockage.
Removing the fan and inspecting the inside of the fan cavity will let you know if there is any blockage.
This I would check first. If the car is not used a lot this can very well be the case.
The bumping noise could be debris in the fan cage or it could be the beginning of the fan beginning to fail.
It is possible that one or more of the control doors may be stuck in the wrong position. It can be difficult to diagnose, this could be one of those jobs for the automotive professional.
There is a service bulletin on blower problems, if is 00-21-3 it is dated 10-16-2000. It is a lengthy bulletin. For the full document you can get it at ALLDATAdiy.com.
I have a 2007 Grand Marquis, the EATC panel will not change the flow. The air only comes out of the window defrosting area
It could be a vacuum line that fell off of the vacuum tank under the hood or the main vacuum lint that supplies the A/C system may of come off under the dash.
If all vacuum lines are intact then it may be an electronic problem with the EATC module.
A mechanic would probably be able to scan the vehicle computer to possibly pull a trouble code and maybe monitor the function of the many doors in the system that could be faulty.
Some vacuum lines are hard to locate, you may want to have a professional mechanic look at this problem.