dash heater vents stop working shortly after car start, other vents are ok

[huntjock]

I've searched the forum and found some good info (http://gmtnation.com/f23/hvac-acuators-dash-removal-2193/). Just wanted to make sure I am headed in the right direction.

Wife's 2003 Envoy has the auto climate controls. She loves the heat blowing in her face during the Winter (now), and the A/C during the Summer. Right now, the heat is blowing through the dash vents just fine for a minute or 2 after starting up the engine. Heat is blowing fine through the floor and defrost vents as well. Cycling through the modes, all is well. Then put it into gear and drive away and it stops blowing through the dash vents. It is as if something closes. The floor and the defrost vents still work fine, if the current mode includes them. Its just the dash vents.

Are we looking at the "airflow mode actuator"? Or what?

Thanks!

 

[The_Roadie]

Welcome! You've done the right research. If you force the airflow mode to the dash vents with the control button, can you get them to blow? If I recall, the normal AUTO mode doesn't use the dash vents, so it does go to the floor more than other vents. A fuse-pull reset might improve the control module's behavior if this isn't right. I'll have to check when I get home to the vehicle. Others should also chime in - what IS the normal behavior of the AUTO mode?

 

[huntjock]

Welcome! You've done the right research. If you force the airflow mode to the dash vents with the control button, can you get them to blow? If I recall, the normal AUTO mode doesn't use the dash vents, so it does go to the floor more than other vents. A fuse-pull reset might improve the control module's behavior if this isn't right. I'll have to check when I get home to the vehicle. Others should also chime in - what IS the normal behavior of the AUTO mode?

If you force the airflow mode to the dash vents with the control button, can you get them to blow? Yessir. They do - for a time. Sit for a while or drive away and no air through the dash vents

Not sure what the fuse-pull reset is. Please advise.

I will try the AUTO mode vs the various combinations again tonight, but it seemed like there was no difference either way.

It did seem as if a little more heat was forced through the defrost vents once the heat stopped coming from the dash vents. I will confirm tonight. Floor seemed consistent - ON was ON and OFF was OFF.

I was going to disconnect the battery after I got home tonight and let it sit for 30+ minutes and reconnect. Not sure that would do anything, but can't hurt, I guess. Waste of time for that?

Big thanks again!

 

[Denali n DOO]

Welcome! You've done the right research. If you force the airflow mode to the dash vents with the control button, can you get them to blow? If I recall, the normal AUTO mode doesn't use the dash vents, so it does go to the floor more than other vents. A fuse-pull reset might improve the control module's behavior if this isn't right. I'll have to check when I get home to the vehicle. Others should also chime in - what IS the normal behavior of the AUTO mode?

My experience is in auto mode the vents will only blow if the system is trying to cool the inside down, when heating up the truck to the set temperature most hot air blows at the feet with some on defrost to keep the windshield clear, in manual mode you can blow at feet and vents at same time but not defrost as well. I always run manual feet and defrost in the winter. In winter using auto, if I crack the window the system tries to warm the inside by blowing heat at your feet and it gets too hot down there. Try the manual mode she may like it better.

also in auto mode the fan won't turn on until the engine is warm enough to blow heat( unless you force it with the fan speed control button). As the engine warms up the fan will ramp up and run on high.

 

[Matt]

My experience is in auto mode the vents will only blow if the system is trying to cool the inside down, when heating up the truck to the set temperature most hot air blows at the feet with some on defrost to keep the windshield clear, in manual mode you can blow at feet and vents at same time but not defrost as well. I always run manual feet and defrost in the winter. In winter using auto, if I crack the window the system tries to warm the inside by blowing heat at your feet and it gets too hot down there. Try the manual mode she may like it better.

also in auto mode the fan won't turn on until the engine is warm enough to blow heat( unless you force it with the fan speed control button). As the engine warms up the fan will ramp up and run on high.

1000%. Exactly the same way mine behaves with the Auto Climate Control.

 

[huntjock]

1000%. Exactly the same way mine behaves with the Auto Climate Control.

Agree with both Denali n DOO and Matt.

After disconnecting the battery for a period of time (~30 min), and then turning the key on but not the engine - and allowing the series of automatic system resets to complete, everything is working as Denali describes.

Shortly after turning on the key there was a big thud somewhere under the dash, then there were some clicks and a grinding noise during the reset. There are still some little noises I've not ever noticed before or paid attention to. Perhaps, something is on its way out. Not sure. But, the manual mode vents are blowing nice and warm in my wife's face - just like she likes it. So, all is well. Thanks for all the help in this forum!!!!!

Neil