Vents Don't Blow Through Dash Please Help

kevinw · April 30, 2009

I replaced the mode door actuator on my 99 gmc sierra 5.3 and ever since the air whether on a/c or heat will only blow out the top and bottom but not through the 4 dash vents not matter where you turn the control knob. The gmc dealer said the mode door actuator can get off a tooth and cause this problem, there is only one way that I see the actuator will go on? Any help please thanks kevin

bill190 · May 1, 2009

If no one knows the answer to your question, the instructions for replacing things like this and troubleshooting things like this would be in a factory service manual set. These are available at a dealer.

My service manual (for my year vehicle) is very brief on this. Just says how to get the actuator in the correct position before installing. Says to connect the electrical connector, turn on ignition, let actuator find its correct position, then install it.

I don't know if the service manual for your vehicle would say the same thing or not?

And my manual does not say anything about fixing a motor which was not synchronized prior to being installed.

With the following, I'm just "guessing", but...

Is the actuator an electric motor with a gear?

Is this is in a spot where you can see what is going on?

Does this mechanically attach with a "keyed" shaft? Or just gears on what you are installing mesh with gears on what you are installing it to?

In other words, if the actuator was not allowed to "find its position" prior to installation, would you still be able to install it? Or would it not fit because the "keyed" connector/gear/whatever would not fit?

Was it synchronized in any way prior to installation?

If just gears, maybe you could remove the motor, manually move the door mechanism to various positions and see what happens. Then move it to a certain position like air out the vents. Then with the actuator still not installed, set your A/C controls for the same (actuator would then be in the same position), then re-install the actuator?

superjim · May 1, 2009

I replaced the mode door actuator on my 99 gmc sierra 5.3 and ever since the air whether on a/c or heat will only blow out the top and bottom but not through the 4 dash vents not matter where you turn the control knob. The gmc dealer said the mode door actuator can get off a tooth and cause this problem, there is only one way that I see the actuator will go on? Any help please thanks kevin

I think that there is a vacuum line that connects to it also.

Make sure it is connected at BOTH ENDS.

On my '99 the vacuum line got brittle with age and heat and broke off at the intake side and the AC was doing that exact same thing.

Zembonez · May 1, 2009

I replaced the mode door actuator on my 99 gmc sierra 5.3 and ever since the air whether on a/c or heat will only blow out the top and bottom but not through the 4 dash vents not matter where you turn the control knob. The gmc dealer said the mode door actuator can get off a tooth and cause this problem, there is only one way that I see the actuator will go on? Any help please thanks kevin

I think that there is a vacuum line that connects to it also.

Make sure it is connected at BOTH ENDS.

Mine got brittle with age and heat and broke off at the intake side and the AC was doing that exact same thing.

+1

For whatever reason it sounds like it isn't opening (or closing) fully.

TyeeMan · May 1, 2009

I had a 99 Silverado and periodically I would get kind of the same symptoms, no air out of the vents, no heat/cool. For whatever reason after I would cycle the key it would fix itself.

I got a subscription to ALLDATA for my truck and there was a data bulletin regarding this same problem. It stated something to the affect that upon assembly some of the wires that go to the hvac controls may be pulled tight and after a period of time you may loose some or all hvac function. The fix was to pull out the controls and releive any tension on tight wires and reasemble.

I would highly recommend that every one get an ALLDATA subscription, go to ALLDATA DIY, it's like $16.00/year or $30.00 for 11 years or some thing like that. Any way, once you have that you will have access to ANY GM data bulletins, customer complaints, parts costs, and of course any and all wiring diagrams, and repair instruction. Best thing I ever purchased!!