Rear HVAC on non-EXT?

Mooseman

Original poster
Moderator
Dec 4, 2011
25,178
Ottawa, ON
I'm hoping somebody can give me a definitive answer to help our fellow member Trailblazer075 in France. He recently had is '02 TB LT's A/C refilled and he is under the impression that he has a front and rear HVAC because he has a rear seat HVAC/radio control, same as my EXT which does have true front and rear A/C. I was under the impression that only EXT's had the true front and rear A/C and that the shorties only had a front system with air ducts from the front system controlled by that rear control. He also does not have the rear fan override switch next to the shifter.

Hopefully the answer is out there as I am afraid that he had his system overfilled.
 

jonbo2002

Member
Sep 27, 2012
213
mine just has a power button on the counsole, it runs at the same speed as the main fan. also I just checked for interchanged for the heatercore on my work program and the ext is the only one that asks front or rear
 

DDonnie

Member
Mar 26, 2012
2,631
Mine has a duct coming from the front, the power button activates an actuator that opens the duct.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Short wheelbase trucks only have one evaporator, up front. The console ductwork is controlled by an actuator in the console, the temperature is the same as the front passenger's side, and there is a boost blower at the bottom of center of the dash. But only for the automatic/digital systems. Manual systems have only a plenum without an aux blower motor. View "A" in the following exploded view shows where the plenum goes. Auto systems have part 10, manual have part 8.

View attachment 28674
 

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DDonnie

Member
Mar 26, 2012
2,631
You've actually given me an idea roadie. Think it would be possible to wire in a 12v computer case fan using the same power switch to give the blower a little boost? I'm getting almost no output on these rear vents.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Assuming you have a manual system without the boost blower, a 12V fan would work fine. But not wired to the resistor pack that the main blower fan is. The low DC voltage it would see may upset the brushless circuit design. Try to get a quiet fan that you can leave on switched 12V all the time.
 

DDonnie

Member
Mar 26, 2012
2,631
In the manual, is the power button communicating with the bcm or is it simply acitvating a servo? I was thinking of just running a relay with power from another source, but I'd like to use the same button. If not, i can always add a switch, no problem.
 

DDonnie

Member
Mar 26, 2012
2,631
I'm at work :raspberry:
 

AtlWrk

Member
Dec 6, 2011
674
For the SWB manual system the rear HVAC controls get a "aux HVAC enable" signal (active ground) from the front HVAC control module but this only tells you if the rear CAN be used, not if it is. From there it is pretty much a standalone controller for the rear mode actuator. In other words, it looks like nothing outside the rear hvac control and the rear mode actuator know if it is on or not.

You could use the enable signal to trigger a relay so that the aux fan is on anytime the system is on.
 

DDonnie

Member
Mar 26, 2012
2,631
Looks like I'm tearing apart the center console again :thumbsup: (I dont even know why i bolt this stuff down anymore)
 

Mooseman

Original poster
Moderator
Dec 4, 2011
25,178
Ottawa, ON
Thanks all for the confirmation. Now I have to let him know that his truck's a/c is overcharged :frown:
 

BRomanJr

Member
Dec 9, 2011
371
Mooseman said:
Thanks all for the confirmation. Now I have to let him know that his truck's a/c is overcharged :frown:

You could also have him check for a sticker that every vehicle should have under the hood stating exact Freon charge for that particular system.
 

Mooseman

Original poster
Moderator
Dec 4, 2011
25,178
Ottawa, ON
Yeah except the sticker is generic and gives both specs.
 

rockfordhx

Member
Jun 24, 2013
1
SO I think that mooseman has his answer though not the one that he wanted. :no: So I was hoping that my first post would be appropirate.

I have a somewhat similar issue to what DDdonnie has, in that the rear AC vents are barely pushing out any air on a 2004 Trailblazer ...

I took apart the center console thinking that it was related to the rear actuator but it appears to be working ok. Then the PWR button is off, there is no air flow. When I power on the rear controls (and the selector is on top vents) I get minimal air output, when i change the selector knob to the floor, I feel that the top vents are off and that the floor vents are open... again low air output....

Here is a video that I took. It was difficult to measure the amount of air being output in order to quantify the 'amount' being discharged....but I remember that when the truck was new that there was a significant air output from the rear top vents...

[video=youtube_share;R6pUBAuvGtg]http://youtu.be/R6pUBAuvGtg[/video]
 

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