This 2009 Mercury Grand Marquis came in with the complaint the air conditioner would only blow air through the defroster vents. Rarely would air come out of the face vents. This is a common problem and can be expensive to repair. A work around, of sorts, is to manually drop the blower speed to the lowest speed setting. Then switch the mode control to the Max A/C position. Slowly bring the blower speed up and note the speed setting when the air shifts from the face vents to the defrost position. Start over again and stop increasing the speed one position lower than when it switch to the defrost position earlier.
To do some testing, the a/c control head will need to be removed from the dash. This will allow access to the vacuum lines at the rear of the unit. Remove the two 10 mm nuts and pull the hose connector from the a/c control assembly.
You can allow the control assembly to hang down while you check the vacuum system. Care should be taken not to damage the wiring, control assembly or dash surfaces.
Using a vacuum gauge connected to the black vacuum hose, check the vacuum signal with the engine running.
There are a couple of ways to test the vacuum actuators. One way is with a short piece of rigid vacuum tubing.
It can be used much as a jumper wire would be used to test a wiring circuit. Connecting the black vacuum supply hose to the blue panel door hose should produce air from the face vents. The engine has to be running and the a/c switched on of course.
The other way to test is to use a hand vacuum pump and manually pump the air out of each line. This will check to see if the corresponding actuator reacts and if there are any leaks. All of the actuators reacted correctly and there were no leaks. The rest of the control assembly was working correctly, so the diagnosis was a faulty control head assembly.
The customer elected to have a new a/c control head assembly installed.
Since I neglected to take pictures of removing the old control head, I thought I would show how it is installed/removed at the end of this repair. Four 7 mm headed screws hold the control assembly in place.
To access the screws the trim panel first needs to be removed.
Using a wide bladed tool similar to what I am using in the pictures below, slide the tool under the panel in the two positions shown. Pry the panel away from the dash to release the spring clips.
After the lower center of the panel is free work towards the outer edges of each side of the trim panel until all of the clips are released. Depending on the options level of the vehicle, there may be several harness connectors that need to be released to completely remove the trim panel from the work area.
I thought I would include a chart of the vacuum hose colors and related actuators.
- White – Air Inlet/Recirculation Door
- Yellow – Floor/Defrost Door
- Red – Floor Door
- Blue – Panel/Face Vent Door
- Black – Source Vacuum
- Empty – Not Used