Rear HVAC Blower Control Module Replacement

cmatt

Original poster
Member
Feb 24, 2012
15
The fan speed control became erratic and then stopped completely in my wife's 03 Envoy XL. Since this is a common issue with these platforms, I documented the replacement in hopes of helping the next person.

Parts needed: Blower control module, AC-Delco 15-72813 or GM 88892976
Tools needed: Screwdrivers, torx bits and sockets.

The rear HVAC module is located behind the trim in the passenger rear. Begin by removing the sill trim at the liftgate and rear passenger door. It's held on with body clips.
EnvoyHVAC001.jpg


Next, remove the anchors for the 2nd and 3rd row seat belts and then the C and D pillar trim. They are also held on with body clips.
EnvoyHVAC006.jpg

EnvoyHVAC003.jpg

EnvoyHVAC005.jpg


Now remove the five screws towards the rear of the large lower trim. Then release the body clips and remove.
EnvoyHVAC002.jpg


So now here's your view (metal bracket already partially removed).
EnvoyHVAC004.jpg


Remove four 10mm bolts holding the black metal bracket and set aside.
EnvoyHVAC007.jpg


The blower control module is located on the back side of the HVAC module. So I loosened the entire assembly, but did not disconnect the HVAC lines. If you follow the wire just behind the fan, you will find the module.
EnvoyHVAC009.jpg

EnvoyHVAC008.jpg

EnvoyHVAC011.jpg


There's a bolt holding the upper and lower ducts that needs to be removed. Here's one of them. Disconnect the ducts from the main assembly.
EnvoyHVAC006.jpg


Now remove the two bolts holding the assembly to the body and the two bolts holding the assembly to the floor (accessed from underneath the vehicle). This is also a good time to ensure the condensation drain is clear of debris.
EnvoyHVAC010.jpg


Pull straight up on the assembly and then towards you. Be mindful of the HVAC lines attached through the floor.
Now you can access the blower control module. Remove to T-15 torx screws and remove the module.
EnvoyHVAC020.jpg


Swap in the new module and reverse steps to install (new on top, old on bottom).
EnvoyHVAC012.jpg
 

Jman423

Administrator
Mar 24, 2014
1,878
United States
Please provide the following information:

Summary:

Vehicle:
Difficulty:
Estimated Time:
Part Numbers:
Cost:
 

cmatt

Original poster
Member
Feb 24, 2012
15
I've tried to reply to your post, but it keeps giving me the "message too short..." error message. So I copied/pasted the answers below.

Jman423 said:
Please provide the following information:

Summary: Repair the rear HVAC fan speed

Vehicle: 2003 GMC Envoy XL SLT I6
Difficulty: Medium
Estimated Time: 1.5hrs
Part Numbers: Blower control module, AC-Delco 15-72813 or GM 88892976
Cost: $65
 

xtremeskier97

Member
Feb 11, 2012
28
When you say the "fan speed control became erratic", are you referring to the knob on the console that allows the driver to control the rear air flow?

If so, that is the exact same thing we are dealing with. First, the number 2 would only work for about 2 minutes then the air would shut off. We'd have to turn it off for a minute then turn it back on to get it to blow again. Then 2 wouldnt work at all, now 1 and 3 are out. Not even the rear controls will turn it on.

Does this sound like the same thing you dealt with?
 

cmatt

Original poster
Member
Feb 24, 2012
15
xtremeskier97 said:
When you say the "fan speed control became erratic", are you referring to the knob on the console that allows the driver to control the rear air flow?

If so, that is the exact same thing we are dealing with. First, the number 2 would only work for about 2 minutes then the air would shut off. We'd have to turn it off for a minute then turn it back on to get it to blow again. Then 2 wouldnt work at all, now 1 and 3 are out. Not even the rear controls will turn it on.

Does this sound like the same thing you dealt with?

Correct. That is the same behavior mine exhibited.
 
Dec 16, 2011
110
cmatt said:
Correct. That is the same behavior mine exhibited.

So if the rear air is blowing from the ceiling but not the console, what is the likely cause?
 

mfancher

Member
Mar 3, 2013
1
Thank you!!!!!!


cmatt said:
The fan speed control became erratic and then stopped completely in my wife's 03 Envoy XL. Since this is a common issue with these platforms, I documented the replacement in hopes of helping the next person.

Parts needed: Blower control module, AC-Delco 15-72813 or GM 88892976
Tools needed: Screwdrivers, torx bits and sockets.

The rear HVAC module is located behind the trim in the passenger rear. Begin by removing the sill trim at the liftgate and rear passenger door. It's held on with body clips.
EnvoyHVAC001.jpg


Next, remove the anchors for the 2nd and 3rd row seat belts and then the C and D pillar trim. They are also held on with body clips.
EnvoyHVAC006.jpg

EnvoyHVAC003.jpg

EnvoyHVAC005.jpg


Now remove the five screws towards the rear of the large lower trim. Then release the body clips and remove.
EnvoyHVAC002.jpg


So now here's your view (metal bracket already partially removed).
EnvoyHVAC004.jpg


Remove four 10mm bolts holding the black metal bracket and set aside.
EnvoyHVAC007.jpg


The blower control module is located on the back side of the HVAC module. So I loosened the entire assembly, but did not disconnect the HVAC lines. If you follow the wire just behind the fan, you will find the module.
EnvoyHVAC009.jpg

EnvoyHVAC008.jpg

EnvoyHVAC011.jpg


There's a bolt holding the upper and lower ducts that needs to be removed. Here's one of them. Disconnect the ducts from the main assembly.
EnvoyHVAC006.jpg


Now remove the two bolts holding the assembly to the body and the two bolts holding the assembly to the floor (accessed from underneath the vehicle). This is also a good time to ensure the condensation drain is clear of debris.
EnvoyHVAC010.jpg


Pull straight up on the assembly and then towards you. Be mindful of the HVAC lines attached through the floor.
Now you can access the blower control module. Remove to T-15 torx screws and remove the module.
EnvoyHVAC020.jpg


Swap in the new module and reverse steps to install (new on top, old on bottom).
EnvoyHVAC012.jpg
 

xtremeskier97

Member
Feb 11, 2012
28
Thanks so much for this info! Finally got around to fixing ours. I'm sure the kids will love it back there again.....and I can have my center vent back again! :wink:
 

dbcooper

Member
Aug 28, 2014
8
Thank you for the post! after I installed the new module (have not put the rear back together) all I get is a clicking sound from the rear end around the fan and modules. Any thoughts?

The issue before replacing this module was that my blower would not turn off when I turned the vehicle off, and I couldn't control the fan speed or where the air would blow from (ceiling or console/floor)

I have a 2006 trailblazer EXT LT with climate control. I also verified that the module you replaced in this post would fit the model trailblazer I have.

Thank you in advance for any suggestions!
 

KNBlazer

Member
Feb 8, 2012
811
dbcooper said:
Thank you for the post! after I installed the new module (have not put the rear back together) all I get is a clicking sound from the rear end around the fan and modules. Any thoughts?

The issue before replacing this module was that my blower would not turn off when I turned the vehicle off, and I couldn't control the fan speed or where the air would blow from (ceiling or console/floor)

I have a 2006 trailblazer EXT LT with climate control. I also verified that the module you replaced in this post would fit the model trailblazer I have.

Thank you in advance for any suggestions!

The most likely scenario is that you had 2 different problems, you now solved one... Now you need to fix the other... The circled in RED modules are the ones that would be clicking, the one that most likely went out is the top one... the bottom one controls the blend of air temp...

Have someone else play with the settings while you narrow down which module it is...

EnvoyHVAC004.jpg
 

dbcooper

Member
Aug 28, 2014
8
Thank you! I will give that a try next - just hope I haven't opened a can of worms by tackling this project myself...

I'll keep you posted with what I find, or if I break something else :hissyfit:
 

KNBlazer

Member
Feb 8, 2012
811
dbcooper said:
Thank you! I will give that a try next - just hope I haven't opened a can of worms by tackling this project myself...

I'll keep you posted with what I find, or if I break something else :hissyfit:
Those modules or actuators go bad when disconnecting the battery.. on my 2004, I had to replace it I think in 2006...

**correction** according to my Amazon history, I bought the actuator in 2008...
 

dbcooper

Member
Aug 28, 2014
8
so, I decided to plug the original module back in, and the blower came back on right away, possibly got a bad module, or am I looking at something much larger?

Again, thank you for your help and pardon any dumb or stupid questions I ask!

**Or could it still be the actuators that are causing part of the problem?
 

KNBlazer

Member
Feb 8, 2012
811
dbcooper said:
so, I decided to plug the original module back in, and the blower came back on right away, possibly got a bad module, or am I looking at something much larger?

Again, thank you for your help and pardon any dumb or stupid questions I ask!
lol...the speed module has to be installed to the assembly, it has a heat sink that must cool off the module, otherwise it doesn't work right...

as far as I think I know...

Module the one in the back, it controls the blower..

the actuators up front, control the temp and vent selection....

both two different things, both two different functions....
 

dbcooper

Member
Aug 28, 2014
8
I understand that aspect, but when I replace the module in back (resistor module) with the new module, that the actuators would only click and the blower wont operate, however when I place the old module back in, the blower runs and the clicking stops.

If I'm not making sense, let me know. :smile: I just might be in over my head on this one...

Granted - I'm an electronic technician, not a mechanic :wink:
 

KNBlazer

Member
Feb 8, 2012
811
dbcooper said:
I understand that aspect, but when I replace the module in back (resistor module) with the new module, that the actuators would only click and the blower wont operate, however when I place the old module back in, the blower runs and the clicking stops.

If I'm not making sense, let me know. :smile: I just might be in over my head on this one...

Granted - I'm an electronic technician, not a mechanic :wink:
Did you use an AcDelco unit? if you did, was it wrapped in a plastic bag?

When I did mine a couple of weeks ago, it was a plug and play .... turned on A/C and it worked fine... I did clean the mating surface on the backside, it had a layer of thermal paste, or remnants of the thermal pad..
 

dbcooper

Member
Aug 28, 2014
8
Yup, as a matter of fact it was the same part number you listed for yours. It was wrapped in plastic when I received it. It does have the thermal material on it, but so did the original. When I tested the unit again with the original, I did not mount it but just had it sit on top of the assembly
 

KNBlazer

Member
Feb 8, 2012
811
dbcooper said:
Yup, as a matter of fact it was the same part number you listed for yours. It was wrapped in plastic when I received it. It does have the thermal material on it, but so did the original. When I tested the unit again with the original, I did not mount it but just had it sit on top of the assembly
hmmm, can't think right now..lol..only thing I can think of is resetting the actuators by killing power... don't know which fuses though..:biggrin:
 

dbcooper

Member
Aug 28, 2014
8
So, apparently not just anyone can plug in the module - you need to have a gift. My buddy watched me demonstrate the issue and so he unplugged the new module and plugged it and the dang thing worked. But I do still need to replace the actuator which I ordered today. Thank you again for your help!
 
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The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
dbcooper said:
So, apparently not just anyone can plug in the module - you need to have a gift.
Typically electronic things respect and obey you more if you know the secret incantation - Ohm's Law. Did you say "Vee equals Eye Arrrrrr" with a pirate's growl?
 
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dbcooper

Member
Aug 28, 2014
8
So, just giving an update. The module works...after the trailblazer runs for about 5 to 10 minutes. Sometimes sooner, but it never starts up immediately - Anyone else notice this? BUT I replaced the temperature actuator (busted the post to the flap), which now works and I'm waiting for the second actuator to come Thursday to replace the actuator for airflow control.
 
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Buckeyebob

Member
May 3, 2016
4
Fort Myers
I have a 2004 Trailblazer EXT LS and the rear fan was erratic then stopped. Would not work on either fan controller. I looked all over for the above detail info of how to remove, but didn't find it from my search. I checked the fan fuse and fan by shorting to ground the black wireof the 2 wires going to the fan which showed the fan was good. I'm adding a couple details. Remove the right middle seat passenger shoulder restraint bolt (large torx), then the top panel pops off, no other screws or bolts. Remove the screws in the side panel at the rear, then the big panel pops off with friction fittings. You need to bow the panel at the back post out from under the top column cover. Remove both upper and lower duct with one screw each (10 mm socket). Remove the metal cover at the rear (holds the screw nuts for the panel) with 2 bolts at the top and 2 more under the carpet at the bed (10 mm). Next remove the 2 bolts holding the HVAC unit to the car (10 mm through rubber vibration dampers) and go under the right rear fender to remove 2 nuts holding the HVAC unit to the floor. This allows you to rotate the unit toward you and access the blower control module which is secured with 2 very small torx head screws.
 

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Last edited by a moderator:

Mooseman

Moderator
Dec 4, 2011
25,561
Ottawa, ON
Welcome to the Nation! Very good first post! I only made a couple small corrections to say "torx" bolts and screws. Probably just an auto-correct snafu.
 

Buckeyebob

Member
May 3, 2016
4
Fort Myers
The rear air control module I replaced last year is a problem again. Only blows on high setting. I presume I need to replace, but could the blower motor be drawing too many amps and causing the problem? Any idea how many amps it should draw?
 
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Mooseman

Moderator
Dec 4, 2011
25,561
Ottawa, ON
Quite possible as the motor ages and bearings get stiff and dry, it takes more amps to spin it.

Was it a new or used module? Used is always a roll of the dice.
 
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Buckeyebob

Member
May 3, 2016
4
Fort Myers
Went ahead and bought a rear blower and new speed control module. Old blower turned as easy as new one. After removal, discovered the new blower housing is totally different so reinstalled the old one. Cleaned off the surface to mount the module, found an extra foil so maybe the previous controlled was not cooled well? At any rate, all is working fine again.
 

TPW1500

Member
Dec 21, 2015
4
South Florida
So, just giving an update. The module works...after the trailblazer runs for about 5 to 10 minutes. Sometimes sooner, but it never starts up immediately - Anyone else notice this? BUT I replaced the temperature actuator (busted the post to the flap), which now works and I'm waiting for the second actuator to come Thursday to replace the actuator for airflow control.
I broke the post on the flap of my '03 Envoy XL as well. I've started to disassemble the the inside facing half of the air chambers only to be stymied by the last screw that holds the two halves together that is located just behind the evaporator tubes (it points upward). How do you get to that screw? All I can think is to disconnect the AC lines (Vac the system dry of freon) to get to the screw, Hope there is a better way.

Also, do you have a part number for the actuator door? - Thx.
 

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