Air flow control

My 05 Mercury Grand Marquis only directs air flow through the defrost and floor ducts. What suggestions do you have to correct this? With 104,000, is it worth it, as it also needs brakes, tires.

Airflow is controlled by flaps within the HVAC system. Something is preventing the flaps from moving as they should. Is this a manually controlled system, or automatic climate control?

104K miles is not much on a Grand Marquis. If it were my car I’d want the air flow control to work as designed, and I’d repair it.

You have a vacuum leak in the AC control system, or a vacuum hose not connected. The airflow (except for the electric blend-air door) doors are vacuum controlled on your Grand Marquis. This is true for manual or automatic climate control.

Thanks, I will check that and hopefully solve it. The mechanic suggested replacing the entire heater-A/C head at about $1400, and that is painful.

I believe we have a duplicate thread here. Check out the other one for additional comments.

Note: It us usually best to put all related problems (even those that might seem un-related) in just one message.

There are two doors that control air flow and one of them has three positions. The first in line, after the heater core, directs air to the panel in one position and to the defrost/floor in the other. The second is the three-position door and directs air to the defrost, or floor or both. In your case, the first door is not going to the proper position. If you have EATC, it cold be a problem with the electronic control unit. With it or without it, you could have a bad vacuum connection or line or a bad vacuum motor. This should be thoroughly checked to eliminate other issues before replacing the EATC unit.

You can see both vacuum motors and their connections by looking up toward the cup holder with your head on the carpet in the driver side foot well. You can access a lot of the connections by pulling the EATC unit and the cup holder.

Diagrams available at

There were a couple of years in the early 00s that had early-failing EATC units, but I don’t recall what years, but tearing into them and replacing the orings will fix them. The EATC unit can be put into a self-check mode and will send out codes. Find out how to do that:

Lots of help available at

Yep, I’d suspect either a vacume leak or a problem with the vacume motor. I had a hose in the engine compartment drop down and get a hole burned in it and had a similar symptom with my Buick. About $2 worth of new hose fixed it. Finding the problem is the hard part. I diagnosed by running a long length of hose from a good source on the engine, and connecting to the HVAC control to determine it was the hose. If that had no effect, I would have had to dig deeper under the dash to the motors themselves.