I have an 05 Envoy and when you have the heat on and set to come out the floor vent only, it comes out the defrost vent also. Also doesn't seem to be moving as much air as it should. The fan runs fine but seems like there is a blockage. On my F-250 when I have the vent issue, it is a vacuum leak. Anyone have any ideas on what I should look for to fix these issues?
Vent control issues
- Thread starter dhanna6
- Start date
Welcome. The HVAC system runs on all electrical actuators, not vacuum powered, but they fail quite often, especially after a battery change or total discharge when they recalibrate themselves after the power comes back.
There are five actuators, and you may have a problem with the defrost or the airflow mode actuators. You might also have debris in the heater core, or in the blower motor impeller housing. The motor is relatively easy to drop from behind the glove box. The actuators are less easy. This site is so new we haven't gotten all the intended "How To" articles up yet, but it all depends on if you're a DIY mechanic who needs help or can poke about on your own.
Here's a picture that may help:
There are five actuators, and you may have a problem with the defrost or the airflow mode actuators. You might also have debris in the heater core, or in the blower motor impeller housing. The motor is relatively easy to drop from behind the glove box. The actuators are less easy. This site is so new we haven't gotten all the intended "How To" articles up yet, but it all depends on if you're a DIY mechanic who needs help or can poke about on your own.
Here's a picture that may help:
the roadie said:Welcome. The HVAC system runs on all electrical actuators, not vacuum powered, but they fail quite often, especially after a battery change or total discharge when they recalibrate themselves after the power comes back.
There are five actuators, and you may have a problem with the defrost or the airflow mode actuators. You might also have debris in the heater core, or in the blower motor impeller housing. The motor is relatively easy to drop from behind the glove box. The actuators are less easy. This site is so new we haven't gotten all the intended "How To" articles up yet, but it all depends on if you're a DIY mechanic who needs help or can poke about on your own.
Here's a picture that may help:
Thanks for the quick response. I do most of my own work but I also have a buddy who is a Tech. at a GM dealership so he could help also. Also, thanks for getting me to this forum. I put your name down as a referral when I joined.
Have also heard that you can use a Tech2 and "rehome" the actuators. Anyone know if this is possible?
Chickenhawk
Member
- Dec 6, 2011
- 782
On both our Trailblazers, the heat is okay but there doesn't seem to be a direct blast of air on our feet when set to floor only.
Is there any way to tell if each of these five actuators is still working properly?
Is there any way to tell if each of these five actuators is still working properly?
I just edited my image links here to the original image. I had changed the stuff that the OS linked to to see how many more folks I could get the message out to. I think that was my most-downloaded image, closely followed by the megafuse. 
You can check the actuators by a simple functional test - move the controls and see if they follow your commands. Airflow mode is the one that chooses floor or dash vents. Recirculate is obvious. Defrost is obvious. Temp is obvious.
Otherwise start pulling dashboard lower covers and observe the shaft on the outside of the actuator turn as you send it commands.
A Tech II can re-home the actuators, but that's another name for the recalibration process you get when you disconnect the battery or pull the HVAC fuse, and I belive it is as risky to weak actuators. You can replace an actuator for less than paying a dealer to touch a Tech II to the vehicle.
You can check the actuators by a simple functional test - move the controls and see if they follow your commands. Airflow mode is the one that chooses floor or dash vents. Recirculate is obvious. Defrost is obvious. Temp is obvious.
Otherwise start pulling dashboard lower covers and observe the shaft on the outside of the actuator turn as you send it commands.
A Tech II can re-home the actuators, but that's another name for the recalibration process you get when you disconnect the battery or pull the HVAC fuse, and I belive it is as risky to weak actuators. You can replace an actuator for less than paying a dealer to touch a Tech II to the vehicle.
the roadie said:I just edited my image links here to the original image. I had changed the stuff that the OS linked to to see how many more folks I could get the message out to. I think that was my most-downloaded image, closely followed by the megafuse.
You can check the actuators by a simple functional test - move the controls and see if they follow your commands. Airflow mode is the one that chooses floor or dash vents. Recirculate is obvious. Defrost is obvious. Temp is obvious.
Otherwise start pulling dashboard lower covers and observe the shaft on the outside of the actuator turn as you send it commands.
A Tech II can re-home the actuators, but that's another name for the recalibration process you get when you disconnect the battery or pull the HVAC fuse, and I belive it is as risky to weak actuators. You can replace an actuator for less than paying a dealer to touch a Tech II to the vehicle.
I have access to a Tech II and I had a voltage issue with the Envoy. I think I'm gonna try that before replacing the actuators.
Chickenhawk
Member
- Dec 6, 2011
- 782
Thanks for the diagram. Everything seems to be working as it should.
It is just funny that my Blazer used to noticeably blast the air at my feet but on our Trailblazers, we don't feel any direct blast of fan-driven air.
Maybe it's just the positioning of the outlets that's different?
It is just funny that my Blazer used to noticeably blast the air at my feet but on our Trailblazers, we don't feel any direct blast of fan-driven air.
Maybe it's just the positioning of the outlets that's different?