low airflow when on heat out of main vents

[matt]

I have an 03 Trailblazer with manual controls and I have very low airflow when on heat mode thru the main vents. It comes out just fine on defrost mode and it blows cold air when in cold mode. Thanks for your help

[TerryAuto]

If the airflow is just low from the center vents, then i would guess most of the air is going to the floor or defrost, even when set on center vents.

This sounds like a faulty mode door actuator. It is not turning the door fully to direct the air from the vents when you want it. It is not that the airflow is low, it is more that it is not being directed to the proper vents. Nothing can limit the amount or air, it has to be going somewhere.

You can try disconnecting the battery for a few minutes. This will reset the door actautor positions in the dash. If that does not help, that actuator would need to be diagnosed to be certain.

[matt]

Thanks foor getting back to me. But when I switch the temperature settings to cold the air comes out of the frot vents just fine. That is what is baffeling me. Could that possibly be a temperature actuator maybe??

[TerryAuto]

Hmm. Just so i am clear...
You switch it to center vents, fan on high, temperature on full cold, the airflow is strong, but on full hot, the airflow gets less?
If that is the case, when it is on full hot, put your hand on the drivers side floor and see if it is coming stronger than when on cold. Sort of have one hand on the floor, turn it from hot to cold with your cheek on the center vent and see if the airflow is changing.

[matt]

Its about the same coming thru the floor vents. Im sure my mode actuator is bad because air comes out of the floor vents in all settings except when it is on defrost mode. And when its on floor setting air comes out of the main ents. When it is on face vents and i change temperatures I can hear the door shut and open as I change the temperature. I ddid the whole disconnect the battery and also removed the HVACB fuse andd did the reset. Am I better off just replacing ALL the actuators? Thank you for al your help. I really appreciate it!

[TerryAuto]

I would just replace the mode door actuator first. That seems to be the problem.
Do that and then do the reset and see how it goes. It seems the mode actuator is problem.
If the truck is new to you, it may have already been replaced, but they do not have it in properly. You have to have the actuator and the door cam sort of timed properly or the positions will not be exatly correct. It cam be kind of tricky.
Some airflow on the floor is normal.
When set to heat, the system tries to put more on the floor- it's made to do that.

[matt]

Well crap! i just replaced that! lol Is there any tips u can give me on how to get it synced right? I think it works but its not lined up right. Before i installed it, i only had air coming out of the defrost vents. I do get air out of the vents just not a whole lot of it when its on the "warm" setting

[TerryAuto]

Well, i wish i had a diagram, but in dont. It is sort of trial and error.
First make sure the electrical connector is NOT connected or you can damage the new one if the motor starts to turn before it is installed.
New ones come centered, so you have to get the door cam- or gear centered as well.

If you have it installed, then you can remove it enough to just get it off the door cam and turn the door cam a bit, then push actutor back on.

[matt]

Ok ill give it a shot.....thanks for all your help. I really appreciate it!