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2003 chevy trailblazer_ls_ext
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Discussion Starter · #1 ·
This is my first post to the forum. I have looked through here before though and have found a lot of useful information. I have a problem with the rear a/c working. It does nothing but blow hot air. The front seems to work just fine and all the positions on the controls work when they should. Late last summer I had to put in a small amount of freon because it was starting to cycle too much and then quit all together. A quick shot of R and it was working fine again. One of my kids that sits in the back will get sick if it gets too hot and stuffy so I really need to get it working and with the economy and all I will fix it myself. I have worked in the automotive field for about 20 years but the last 15 I was doing auto glass so I am not afraid to dig into anything. Any suggestions or help would be appreciated very much. :)
 

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Details about your truck would help (you should fill out your profile in the user CP, so we don't have to ask again). Is it a long wheelbase (EXT/XL) truck? If so, is the problem only with the upper vents?

Joe
 

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Did you try resetting the system? Disconnect the battery or pull the fuse for the HVAC. I don't remember the exact number, but it will be in the owner's manual or do a search on this forum.

If that doesn't work then you probably have a problem with the rear actuators.
 

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A quick shot of R and it was working fine again.
Without fixing the root cause (the leak), this is not a repair. Unless you have all the professional leak testing and vacuum equipment, this really isn't a DIY item. You may need a pro.

It might also be a rear temp actuator, so I'd start with taking apart the right rear side panels to get at the HVAC unit, then run the reset procedure. Depends on your vehicle, but I'm guessing fuse #36 in the rear fuse block. WIth the ignition off, pull it for 30 seconds. Then put it in, and turn on the ignition but not the engine. Don't touch any HVAC controls for 90 seconds, and observe all the actuators go from end to end to recalibrate their rotational position sensors. If you have a problem with the rear heat actuator (item #33), it will blow hot even if cold air is available at the evaporator.

With bad refrigerant level, of course, the evaporator (item #16) won't be cold.

http://www.compnine.com/index.php?u...delid=7132&capuid=1&majorgroup=09&grouptype=B

 

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Discussion Starter · #5 ·
I did the reset and when you do it you can see and hear the actuator moving. After I wait and fire it up it seems to blow cold air for a few minutes but then it starts to get warm and almost hot. This is coming from the upper vents. The front a/c works fine is and good and cold. When the rear actuator resets it sounds like it kind of comes to a slow halt instead of a making a noise like a door flapping shut. Maybe it is just coming against the seal? I would think that if the front is good and cold that it should be some sort of mechanical problem but I hate replacing parts without knowing I have the right one with 90% certainty.
 

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Discussion Starter · #7 · (Edited)
Here is what I have noticed so far. The floor to overhead controls work fine. When I start the car up and turn it to a/c it seems to work fine for about a minute or two. Then I notice that the temp blend actuator will turn all the way to heat apparently and it will start to get warm then. When you shut it off for a few minutes and start it up again the same thing will happen. :bonk:

I took the motor off and forced it over to cool and it was working fine. So now is it a bad motor or something that controls that motor that is making it turn back to heat? Oh by the way, when you said to remove the actuator from the door you forgot to mention be careful not to snap off the end of the blend door end in the motor. :bonk: :bonk: Got a little impatient trying to get it off.
 

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Could be a bad actuator or rear control module. Without measuring the voltages on the actuator control connector, or taking it to the dealer with their scan tool, it's not possible to guess which one. You could interchange the actuators as an experiment, since they're the same part number. That would home in on the bug.
 

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Automatic A/C reset??

Hi, i've tried to reset te rear HVAC some days ago, and i've read that you remove the fuse, wait, put it again, and switch the key without starting enige and touching any A/C controls. But I have an TB EXL 2005, with the automatic digital A/C, so when switch the key, the A/C starts to work on AUTO mode and sends cold air on the front. Is it ok for the reset or should i stop or block the auto A/C to reset?? any suggestions??

My problem is that rear A/C works ok only in the floor vents, in the ceeling just blows normal warm air, not cold, not hot. everything else is fine. Any suggestions besides de reset?
 

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The reset REQUIRES the system to go through its paces. Don't stop it.

If the rear doesn't start behaving properly after a reset, take off the interior panels and see which actuator is not moving when commanded. I've posted this picture in many, many other threads over the years discussing rear actuators (a fruitful search phrase).

 

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With air flow, an easy check to see if the rear air flow actuator is working without taking the back panel apart is to turn the heat on and see what happens when you direct the heat through the vents or to the floor.
 

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With air flow, an easy check to see if the rear air flow actuator is working without taking the back panel apart is to turn the heat on and see what happens when you direct the heat through the vents or to the floor.
Thanks for the idea, ohhhh well, when i turn the heat to the floor vents, it works ok too. The problem is just in the ceeiling vents. Any idea???
I'll start to think about remove the panles to chec the actuators if there's no other choice, but I wanna try everything before ripping my tb. :(

And Roadie, thanks for the pic, Just want to know exactly what to check before dissasembly or change.
 

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Thanks for the idea, ohhhh well, when i turn the heat to the floor vents, it works ok too. The problem is just in the ceeiling vents. Any idea???
I'll start to think about remove the panels to check the actuators if there's no other choice, but I wanna try everything before ripping my tb. :(

And Roadie, thanks for the pic, Just want to know exactly what to check before dissasembly or change.
So what are you saying? When you direct air to the floor vents, the rear will follow unless you've turned the controls over to the rear seat. When you direct the air flow through the dash vents (not the floor) and the rear blower is on, the rear air flow should be through the ceiling. If that's not happening, then you have a bad actuator.
 

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Will this help me.

Noob here on the site. Thanks to all who have conntributed to me joining today.

Have the thumping issues on the Rear passenger side it was just intermitently.

Now is for the first minute or two no matter what I have going with the HVAC.

Also once it changed to always doing it. The rear AC is not blowing cold air.

Found the post about the actuators If i replace both these ACDelco 15-72811
Should that resolve both issues?

Have no front A/C issues...

Any advice would be awesome!!!
 

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Only change the actuator that's failed unless you like to waste money. One is for temperature. The other for airflow direction. Which one is which is sort of obvious by their positions in the plenum.
 

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Only change the actuator that's failed unless you like to waste money. One is for temperature. The other for airflow direction. Which one is which is sort of obvious by their positions in the plenum.
Just to make sure I am good... Did further testing... Cold air on the floor... Hot air in the roof... Cold air up front...

Get 1 actuator and replace and it should fix thumoing and Hot air on top?

Sorry if I am being dense... :)
 

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Are you changing just ONE control at a time?

If you have airflow on the floor and change the TEMP control, does it change from cold to hot and still blow on the floor level?

If you have COLD airflow on the floor and change the AIRFLOW control, do you get COLD airflow on the upper level?
 
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