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2005 Grand Marquis HVAC goofy

13K views 10 replies 3 participants last post by  Bajarider 
#1 ·
I just got a 2005 Merc GM LS (Saturday, 1/28/12). It has 91000 miles (after 650 miles of joyriding in 2 days). It has the EATC. It blows mostly thru the dash vents. When I select defrost I get a little out at the windshield. I get a little at the floor when I select floor. I have already replaced the O-Rings in the control module. I can see the actuators opening and closing the flappers (it didn't do that before I replaced the O-Rings). I do seem to have control over the temperature. I cannot hear any vacuum leaks anywhere. I don't know what else to try.
 
#2 ·
Try the self test, press the OFF and DEFROST buttons at the same time and release, then press the AUTO button within 2 seconds. The display will show a flashing blower icon for 20 seconds, after which all vacuum fluorescent segments will be displayed if there are no on-demand DTCs present. If DTCs are present, the HVAC module - EATC will display "00 00" and then on-demand DTCs.
 
#3 ·
I pressed off and defrost at the same time and then the auto button, but every time it only turned on the system in auto mode - no self diagnostic. Off seems to turn it off, and defrost lights up the defrost icon, and auto says "auto", so I believe that the buttons are functioning, but I cannot get a self test. Does the car need to be off? Accessory? Running?
 
#6 ·
I am going from memory of about five years ago, but I recall that there were three vacuum motors in the system. I don't think you would get a TC if one of the motors (cans?) had a leak, and you would probably get the symptoms mentioned if there was a leak, the panel door was stuck or leaking, or the panel vacuum motor was leaking. Are you sure you hear the panel door open or close solidly when switching from vent to floor? The panel door diverts air flow from the defrost/floor to the dash vents.
 
#7 ·
There are 2 'cans' or actuators behind the control unit, and another on the passenger side that closes off the outside air. Is there another? I cannot hear the vent door close, but I can see the actuator move the control lever for the flap.
 
#8 ·
You are correct regarding the actuators. My panel, or vent, door closes firmly with a barely audible "clunk" on all our ford cars and truck and I think this is normal operation. It wasn't always that way on the '01GM. The door sometimes rattled, my dash vents were always on and the door closed slowly. I too replaced the 'O" rings, with no change.

It's a real chore to remove the dash, but I finally "bit the bullet" and tore it apart. I found that the panel door had cracked near a hinge point. I replaced the heater core, blend door actuator and the entire plenum, the first two items just because they can sometimes cause problems, and all has been well for over five years now. The parts, especially the plenum, are expensive, but I didn't want to pull the dash again, ever! Plan on two or three days of part time work, taking your time, to do this. It can surely be done faster, but better to take your time.

It's not necessary, unless you are a pretzel, but I even removed the front seat to make working under the dash easier. This also keeps the leather from being damaged.

Bert recommended just removing the right side of the dash and loosening the left, to gain access to the plenum. His way makes sense, but I didn't know about this site then.
 
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