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50 Posts
Discussion Starter #1
This guide is mainly for the poor guys just delving into finding the cause of vent air flow problems. Welcome to the vent door labyrinth.

The 5th gen vent system consists of three vent doors that open and closes mechanically via three separate vacuum motors (sometimes called a vacuum actuator or pod).

These include: 1. Recirculation door, located behind the glove box. The pancake metal disc is the vacuum motor. When vacuum is applied to this actuator the recirculation door will open allowing air to be drawn from the cabin through the blower motor and back into the duct manifold. While in the open position the same door will partially close the external air intake (outside just below the windshield covered by the screen) GM designed this door to only partially close off the outside air intake so that fresh air would clear any potential build up of toxic gasses that might enter the cabin.

2. A/C Heater door. This is the lower door which sits behind the radio. This door actually is normally relaxed half way between closing off the heating vent and closing off airflow to the upper side of the system (dash vents/defrost). The actuator that moves this door is two sided, that is there is a vac line (yellow) which closes the heat vent and another vac line (Red) which pulls the door up to close off airflow to the upper plenum.

3. A/C Defrost door. This is the upper door which you can see (depending on it's position) through the center dash vents. This door is normally in a position which closes off the dash vents and directs air to the defrost vent.
One can see from the above descriptions, that if vacuum is not present all the doors would be in their normal position and that air flow would come from the outside of the car, pass through the lower plenum with some air blowing out the heater vent and some air blowing through the upper plenum being directed by the normally positioned upper door to go out the defrost vents.

There are many ways to troubleshoot. The following should help you through all the possibilities with minimal invasive parts removal. It follows an "ease of access" flowchart rather than following "the working path" of the system.

Step 1. Confirm Vacuum source. Open glove box completely. Locate the recirculation door and actuator. The door is the vertical panel just behind the actuator. Turn on your engine (to produce a vacuum) and move the upper slider on the control through all its settings. Count to 10 in each setting as the actuators take a little time to actually pull vacuum. This door should open (and you can clearly see it open) only when the slider is in the MAX position. If it opens on Max only, you
know that a. you have vacuum to your system. b. Your switch is being turned correctly by the control lever. c. The recirculation door and actuator are both working.
If this door works as it's supposed to, skip step 2.

Step 2. Follow the orange vac line coming from the recirculation door actuator. It will go into the female side of a plastic coupler with other vacuum lines. Carefully open this coupler separating the two sides. Using a hand vacuum pump or vacuum gauge, with engine running, check that you have vacuum on the purple (female side) of coupler. Good vacuum (>15) tells you that your under hood vacuum lines are ok.
If good Go to step 3.

2b. Under the hood, Find the vacuum canister (softball sized round canister). The vac line in which we are interest should come out the top of the vacuum canister on the right side. Trace this line from the canister and actually feel and bend it. It often gets brittle and cracks. If it is brittle keep tracing it until it gets pliable again. Cut and replace the bad length. Confirm you have vacuum at the canister (with engine running). Go back to step 1.

Step 3a. Confirm that the actuator and recirculation door works manually. Using a hand vacuum pump (I use mightyvac with gauge), place the mightyvac lead into the orange line on the female side of the connector, pump up the mighty vac to 15 and watch the recirculation door. If you see it open, wait 15 sec to make sure the actuator does not lose vacuum. If it stays open you know that the door and actuator work properly. Now is a good time to check to see if you can tell if there are any gaps around the edge of the door when this door is closed. Air should not be pulled from the interior when this door is closed.

Step 3b. Confirm that the actuator and lower heater vent door works manually. With the key in "on" position (car does not need to be running) and upper AC control set to vent, turn blower switch to high level. Using a hand vacuum pump, place the mightyvac lead into the yellow line on the female side of the connector, pump up the mighty vac to 15 and place your hand under the lower heater vent, you should feel the airflow cut off when vacuum is applied to the yellow line. If airflow reduced but still blows any significant amount, you have lost the foam weather-stripping that seals this door closed. If you have loss of airflow, wait 15 sec to make sure the actuator does not lose vacuum.

Next, switch the mightyvac to the red line. You should feel the airflow increase to more than it does when no vacuum is applied. Wait 15 sec to make sure the actuator does not lose vacuum. If it stays closed you know that the door and actuator work properly.

Step 3c. Confirm that the dash vent door and actuator works manually. Using a hand vacuum pump, place the mightyvac lead into the blue line on the female side of the connector, pump up the mighty vac to 15 and watch with a flashlight through the dash center vents, this door can be seen as it opens. If you see it open, wait 15 sec to make sure the actuator does not lose vacuum. If it stays open you know that the door and actuator work properly.

Step 3 Repairs. If you had lost vacuum during your 15 sec wait, it's time to replace the actuator.
If any of the doors did not operate you will first want to see if the door themselves are just stuck.
I have not heard anyone say that their doors actually broke. But many have said that the old foam weather-strip had deteriorated and caused the doors to stick.
The recirculation door is easy, you can press on the door just below the actuator (the actuator actually looks like the back half of it goes through the door. Pressing just below the actuator will pivot the door up (the hinge is along the top side of the door. It should move pretty easily with no more pressure than lifting a glass mug of beer :). You can see the weather-stripping around the edge of the door. Once this door breaks free and moves freely, check with manual vacuum again to see if it opens via the actuator.

50 Posts
Discussion Starter #2
Troubleshooting 5th Gen AC/Heat Vent Door Part 2

The lower heat door is harder to get to. Some say to remove the radio first, I was able to get to it by crawling under and removing a screw from the plastic vent guide that comes in contact with the carpet, centered over the hump. The screw is a 9/32" socket aiming straight toward the rear of the car in the center of this vent guide. There is a second screw on this plastic guide on the passenger side of the hump with the head pointing down. Once this is off you can see the door by looking up into the vent plenum. Mightyvac the red vac line and press the door up on the passenger side (it is hinged on the driver side. The weather-stripping is known to deteriorate most on this door due to additional heat that it is exposed to from the heating system. Once you get it to move freely, confirm if the actuator can move it. In almost all cases you will want to replace the weather-stripping so that this door will completely close when in the down position.

The upper vent/defrost door is gotten to from under the hood of the car. (I have not personally had to do this) I was told that you get to it via removing the top of the heater box. Be careful, this lid is sealed and will need to be re-sealed.

Some have mentioned spraying lubricant onto the hinge of the dash vent door from the dash vent opening has done the trick. (Anyone that has corrected this part of the problem, please write up the solution.)

Spray lubrication onto the door hinges and remove all deteriorated weather-stripping and replace. Your doors should now work with manual vacuum. Reconnect the multi-port connector behind the glove box.

Step 4. R&R nine port switch, Located at the rear of the AC control, toward right side.
Remove the face plate covering the radio and AC control unit. Besides the visible screws, there is a clip holding the cig lighter, once you start to get it loose you can reach behind and open the clip to disengage the lighter.

Unscrew the AC control unit (4 screws). Pull straight out. Protect your radio with a rag.
Remove the illumination light by turning slightly. Just behind the faceplate right side.

Remove the 2 port connector (rear, top left side) by lifting straight up).
Remove the center electrical connector. There is a clip on top center of the connector.
The only connections remaining should be the vacuum lines to the nine port switch and the cold/hot control cable.
I was able to leave the control cable attached by helping make some slack in it's path so I could pull out the unit just far enough to remove the vacuum line connector from the nine port switch.

Removing the nine port switch. There are two locating poles in which the rubber vac line connector attach to. I remove the holding clips with a door panel remove tool. In any case just work it (them) from all sides evenly to remove. The rubber connector will now simply pull off.

Notice how the switch is moved by the pin from the control unit. On the lower side, there is a screw which holds the nine port switch onto the control unit. Remove and take off the nine port switch. Move the upper control lever and watch the movement of the pin. If it moves as you move the control arm, you know the control unit works (at least for the vent door operations).

Take apart the nine port switch. You will see the blatter with the maze of ridges that change vacuum direction to different ports.
Sometimes debris gets into these channels. If you see debris you may be able to clean this blatter with a tooth brush and reinstall.

The lines from it to the connector behind the glove box may be losing vacuum. It's easy to take the vacuum line harness out now and make sure each colored line is clear and via the mightyvac and plugging one side, you can confirm all lines in it hold vacuum. If all lines are good, replace the switch. Reinstall.

If it looked clean to you at first, it may be that the rubber has just become more brittle and allows vacuum to escape. I would recommend cleaning the blatter and replacing it. Hook every thing back up and test it without actually bolting the unit back in. If it continues to fail, it's time for a new nine-port switch.

20 Posts
What makes the center flap door vent to open? I can manually reach in there and pull it up which then air comes thru to the center vents. Once I open that vent door, I see a triangular door vent further down. I am able to push it down and up? What I need to know how do these vent doors operate or what makes them open or close? What actuator do I need to check? i am not getting any air thru the center vents. See foto's. BTW, I also found a metal hook inside when I opened the center door vent. Any ideas? See foto


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