2004 Tahoe AC goes to heat in both front and rear

[Alan's Classic]

Some days with the AC on in front and rear, one or the other will go to heat (hot). It will stay that way until the key is turned off and restarted. It has dual zone control in the front and the driver side goes to heat and the passenger stays in AC.

I thought it might be a blend issue, but since it does it in the rear also I believe it is more of a control issue. Ideas.

I did service it thinking the freon was low.

I did a search, but didn't find anything like this. Thanks

[clinebarger]

Originally Posted by Alan's Classic

Some days with the AC on in front and rear, one or the other will go to heat (hot). It will stay that way until the key is turned off and restarted. It has dual zone control in the front and the driver side goes to heat and the passenger stays in AC.

I thought it might be a blend issue, but since it does it in the rear also I believe it is more of a control issue. Ideas.

I did service it thinking the freon was low.

I did a search, but didn't find anything like this. Thanks

The left front & rear blend door motor's could be bad. It resetting tells me there are codes in the HVAC module, A GM Tech II is the only scan tool I know of that can retrieve them.

[Alan's Classic]

Originally Posted by clinebarger

The left front & rear blend door motor's could be bad. It resetting tells me there are codes in the HVAC module, A GM Tech II is the only scan tool I know of that can retrieve them.

Thanks, I'll see if I can find a buddy that has one. I'll update when I find out something.

[Alan's Classic]

Found someone that can scan it, but he couldn't do it today. He did tell me to pull the hvac fuse out for 30 secs, install, and start truck. Then let it idle for 40 secs without touching the controls so it could calibrate. The problem is worse now. I should be able to have it reflashed tomorrow. He said if that doesn't the next step is a control panel.
Posted via Mobile Device

[Alan's Classic]

A buddy of mine is a senoir tech at our local GM dealer. He checked and had one code "loss of data" He reprogrammed and so far so good. He said if the problem comes back the Drivers blend door and the rear module might need to be replaced.

BTW he said pulling the HVAC fuse doesn't do anything for it. If that's true or not, i don't know.

If the problems come back I will update this thread.

[Alan's Classic]

Update:

The front still remains fine; however, the rear is another story.

It started blowing cold air and no heat. Here are the steps I went thru to repair.

1.The blend door would over drive itself to the cold mode. Replaced the blend door actuator. No change.

2. Tech 2 scanner found code PO434 (I think that was it) Replaced control module (old PN 15185966) with (new PN 15832319). That enabled the blend door too move, but still ended up in cold. This really baffled the GM guy. He said that normally fixes it.

3. Scanned again and had code PO429. The code had something to do with the temp probe. There is actually 2 of these. One in the floor duct and one in the ceiling duct right behind the C pillar upper trim. We replaced it and all is well.

4. Just for curioustity I installed the old blend door actuator and it works fine.

[Mr.960]

Hello Alan,

Bumping an old thread. May you please give me the part number of that temp probe sensor? My parts man does not show it on his diagrams, and my truck has it. Also, did you replace the one for the floor vent, or the roof vents?

Thanks!!

[Alan's Classic]

I wish I could help but the part number. The mechanic had a parts truck that he swapped it out. It was for the roof vents.

[Mr.960]

okay, do you have to remove the c pillar (sail panel) or the headliner to gain access to that bugger?

Thanks!

Mr. 960

[Alan's Classic]

Sail panel trim on C pillar

[Crummy]

Mine does this occasionally but it is only the driver's side that blows hot air. Griped the crap out of me. I found if you slowly cycle the temp controls from cold to hot back to cold it will reset. That took too much time. I can shut it off and crank it back, Fixed!!!

Any ideas? Winter now so not an issue now. But Summer will come again.(only did this about 5 times all summer)

[Alan's Classic]

Originally Posted by Crummy

Mine does this occasionally but it is only the driver's side that blows hot air. Griped the crap out of me. I found if you slowly cycle the temp controls from cold to hot back to cold it will reset. That took too much time. I can shut it off and crank it back, Fixed!!!

Any ideas? Winter now so not an issue now. But Summer will come again.(only did this about 5 times all summer)

That's what mine has done in the front for the past year and progressively gotten worse to the point the right is AC and the drivers is heat. I can hear the passenger blend door popping like it is in a bind. I can put my hand on it, but the drivers side is another story. It's not my daily driver anymore so it's low priority now.

[Mr.960]

Yea, I put the new rear control module and that seems to have fixed it for now. However, when I first put the new module on it would only blow through the roof vents; the temperature control was fine. I had to unplug it then plug it in and that has taken care of it, until last night when it did it again; stuck on roof vents. At least I can still control the heat. My original problem was stuck on cold only. I did the nut and bolt on the temp actuator to keep it from over traveling; it worked great for 3 years. Then I had the get stuck on HOT problem, that shutting truck off then back on would fix - every time! Ever since the new module the temperature control is fine. Now it seems the actuator for the roof and floor control sometimes get a little stupid and gets stuck on roof, but I can live with it, so long as I can still regulate the temperature.

Mr. 960

[68 TT]

I have been living with this same problem on mine for eight years. Too cheap to pay what the dealer wanted to fix it. Years ago they told me the fix was to reprogram the Auxiliary HVAC Control Module and replace all the actuators. $500 just to reprogram the control module plus all the actuators and the labor to do it came to nearly $1000. Needless to say I did not do it.

I unplugged the blend door actuator from the harness and put the blend door to heat and aligned the actuator to match so I could have rear heat in the winter. For the summer I can just plug the actuator back in and it cycles to full cold all on its own.

I hadn't thought about this repair again until just today. I didn't think there was any other way to fix it.

I found a video just a little while ago showing what part needs replaced and what does not.

https://www.youtube.com/watch?v=y4-WlE6-Nkc

I didn't see why the stealership said I had to replace all the actuators when they seemed to work just fine. I was right. Nothing was wrong with mine. The blend door actuator was being told to over travel by the defective control module. Just the usual fleecing of the consumer that they think they have over a barrel.

Also found a great price on the AC Delco 15-73506 equivalent of the second design GM 15832319 Auxiliary HVAC Control Module.

Amazon.com: ACDelco 15-73506 Control Module Kit:...


I found this copy of a GM tech document on another site that explains it all plus a little more.

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#06-01-39-015A: Unable to Control Rear HVAC Temperature or Modes, Intermittent Ticking Noise from Rear HVAC Actuators or Rear HVAC DTCs B0434 or B3764 (Replace Auxiliary HVAC Control Module) - (Jan 12, 2007)


Subject: Unable To Control Rear HVAC Temperature Or Modes, Intermittent Ticking Noise From Rear HVAC Actuators Or Rear HVAC DTCs B0434 Or B3764 (Replace Auxiliary HVAC Control Module)


Models: 2003-2006 Cadillac Escalade Models

2003-2006 Chevrolet Suburban, Tahoe

2003-2006 GMC Yukon Models

with Automatic Control HVAC System and Rear A/C (RPOs CJ2 and C69)




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This bulletin is being revised to correct one of the blower motor control module part numbers. Please discard Corporate Bulletin Number 06-01-39-015 (Section 01 -- HVAC).


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Condition
Some customers may comment on one or more of the following conditions:

• An intermittent ticking/clicking noise from the rear Heating, Ventilation and Air Conditioning (HVAC) system.

• Unable to control rear HVAC system temperature.

• Unable to change rear HVAC system modes.

Technicians may find that Diagnostic Trouble Codes (DTCs) B0434 and/or B3764 have been set.

Cause
These conditions may be caused by HVAC actuators that hunt for the correct position. This cycling may cause a clicking or ticking noise.

An overtravel of the HVAC system control doors may cause one or more of the above system conditions. If an overtravel occurs, a DTC will be set, and the door will go to a preset default position.

When a system door defaults, that door will stay at the default position until the DTC is cleared. Clearing the DTC will allow the door to operate properly until the overtravel condition reoccurs. The following table lists the DTCs that may have been set and the door that is associated with that code.

Overtravel DTC
System Door Affected

B0434
Auxiliary (rear) Air Temperature Actuator

B3764
Auxiliary (rear) Mode Actuator


Correction
Technicians are to replace the auxiliary (rear) HVAC control module with the part number listed in the table below. Refer to the Auxiliary Heater and Air Conditioning Control Module Replacement procedure in SI for more information. This module contains a new calibration to compensate for the actuator overtravel condition and the hunting/clicking noises. The new calibration effectively eliminates DTCs B0434 and B3764. The new control module also eliminates the default position of the doors associated with the DTC. The new control module will allow door travel from counts 0 to 255 without setting a DTC or defaulting the door.

The new auxiliary HVAC control module is compatible with either the first or second design blower motor control module. When using the new auxiliary HVAC control module, the customer may notice a slight increase in the rear blower motor speed (approximately 50 rpm) at a given setting, as compared to the blower motor speed at the same setting with the original HVAC control module. If the customer comments that the increase in blower speed at a given setting is objectionable, the blower motor control module may be replaced with the second design part listed below to correct the slight increase in speed.

The revised auxiliary HVAC control module should not be used unless one or both of the DTCs are set or one or more of the conditions listed above are present. The revised auxiliary HVAC control module will not correct any other DTC or Air Conditioning (A/C) performance concern.

Parts Information
Auxiliary HVAC Control Module Part Number
Description
Qty

15832319
Module Assembly-Auxiliary Heater & A/C Control
1


The blower motor control modules listed below should not be used unless the customer finds the change in blower speeds between the original and the new auxiliary HVAC control modules objectionable.

Blower Motor Control Modules Part Number
Part Description
Vehicle Application
Quantity

89024926
Module Assembly, Auxiliary Heater & A/C Control (Auxiliary Blower Motor Control Module) (Second Design)
Escalade, Tahoe, Yukon (vehicles with a short wheelbase)
1

89018849
Module Assembly, Auxiliary Heater & A/C Control (Auxiliary Blower Motor Control Module) (Second Design)
Escalade ESV, Suburban, Yukon XL (vehicles with a long wheelbase)
1
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Hope this helps somebody else figure this out as well.

[anubisani]

ok I just fixed mines today actually 5 mins ago I had only heat blowing out the defrost vents on driver side and mild cold air on driver side defrost vents . but my rear a/c was working fine. 1st thing to check is the blend door actuator on the passenger side make sure it is working , take it out and change the controls and see if the center piece moves , if it does remember the original position and use a plier and turn it back to where it was so you can get it back in . before you plug it back in remove 10 hvac fuse on driver side , remove 30amp fuse also . go under hood an remove the other 10 amp hvac fuse. put the actuator back plug it in put all fuses back then turn the truck on but do not start make sure a/c switches are off , you should here the doors moving around wait 3 minutes for this process then turn truck off then start and it should be blowing cold air . I just did this like 30 mins ago ,my a/c was stuck in defrost vents for 1.5 years after I had a dead battery and here in fl you need a/c . hope this works for you .