Hvac Doors Out Of Calibration

mackskibum · July 27, 2008

Good morning. I have been researchimg a problem for the last several days,and have not seen a symptom description that matches mine.

2005 1500 Silverado 4x4 LT Automatic temp control.

Had a dead battery on Thursday- left my GPS turned on for a week. Was dead as a stone. Charged battey, started engine. HVAC now blows only hot air- as though the control for both sides is set at 90 degrees.

Read a bunch of stuff on the net- I have removed the HVAC-ECAS fuse several times and attempted door actuator recalibration. I got heat from both sides- made no difference. On second recal, I had AC on the left, heat on the right. On the third recal, I had AC on the right, heat on the left. On the 4th, I had heat on both sides again.

If I manually change airflow direction, I can change from defrost to heat to dash vent. Fan speeds change OK. I can't seem to get all the doors to return to the correct position at the same time.

Any suggestions?

Thanks in advance for your help

Best.

Dave

minibike132 · July 28, 2008

Removing the fuse is the alternate recalibrate. A better way is to perform a recalibration with a tech-2 scan tool. I assume you don't want to spend any money though so all you can really do is the procedure you are already doing but leave the fuse out longer and do not tuch any of the controls for atleast a minuite while they are learning the calibration. Then once the minute or longer is done turn the key and engine off and open and close the door to simulate a run cycle finished. Leave the door closed for another minute and then get in and start the truck, hopefully at this point they will have relearned. Good luck.

mackskibum · July 29, 2008

Thanks Sparks. The additional procedures you mentioned were not in the Alldata information- no information was included about engine shutdown and open/close door to simulate a use cycle. I don't mind taking something to a technician- i just like to try to fix it myself- there's not much I can't solve without a little info.

I am a pretty advanced shadetree guy- I just get stuck sometimes and need a little help. I have a software package that allows OBDII info and interface to BCM, TCM, etc. It has bi-directional control capabilities, just not the TechII calibration abilities.

I was able to get this corrected- either by being lucky or just hitting it right. I cleared one DTC from the HVAC module related to a door position overrun. I then actuated the left and right blend doors with my software. Once that was done, the system has been functioning normally- I ran these tests yesterday.

I really appreciate the time you guys donate to the board- it's a big help to us weekenders out here

Best,

Dave

minibike132 · July 29, 2008

Glad you got it fixed. Our manuals don't always give us those extra steps either it's just something you learn they have left out after getting burned for a couple of hours doing it how you were told. On that system when you key up after reinitalizing power to the module the relearning that is happening is the module sweeping the actuators to the extremes and learning where full hot, full cold, recirculation, fresh air etc. If you give the module a command by turning the temp up or down it aborts the learn and assumes it must be known and valid. Anytime you have to recal or learn something it is a good idea to power down and make the vehicle think a drive cycle has been completed before getting back in and firing it up. Most times it doesn't matter but when it does (and they usually don't tell you when that is) missing that step can send you chasing your tail for what seems like forever.

Z71Fan · August 18, 2008

Glad you got it fixed. Our manuals don't always give us those extra steps either it's just something you learn they have left out after getting burned for a couple of hours doing it how you were told. On that system when you key up after reinitalizing power to the module the relearning that is happening is the module sweeping the actuators to the extremes and learning where full hot, full cold, recirculation, fresh air etc. If you give the module a command by turning the temp up or down it aborts the learn and assumes it must be known and valid. Anytime you have to recal or learn something it is a good idea to power down and make the vehicle think a drive cycle has been completed before getting back in and firing it up. Most times it doesn't matter but when it does (and they usually don't tell you when that is) missing that step can send you chasing your tail for what seems like forever.

Ok. I've got a similar problem and tried to fix it as described above. Maybe I don't understand some details because it didn't work.

I have an '04 Silverado and I replaced the battery yesterday. Today, the HVAC system blows hot air out the drivers side and cold air out the passenger side. I don't believe it is a coincidence that the two events happened together.

I disconnected the HVAC/ECAS fuse for a minute from the fuse box under the hood. Then I got in and started the truck. The AC was automatically on the Auto mode and set at 74 degrees. I let it run without touching for a minute and a half. Then I shut off the truck, opened and closed the door for a minute and restarted the truck. No change to my HVAC. I have no idea at all what opening and closing the door does for the setup. Maybe it was supposed to be vent doors but I have no idea and didn't glean that info from above text.

Did I do something wrong? Any clarification would help.

This is my first post here and I look forward to any and all interactions.

Thanks.

Z71 Fan

minibike132 · August 19, 2008

Do it again but remove the HVAC/ECAS fuse in the underhood fuse block and HVAC1 fuse in the left instrument panel fuse box, and do it for longer than a minuite, go have some dinner or coffee.

As far as the door thing goes I meant the driver door, it may or may not do anything for this module but sometimes modules need to see a drive cycle completed. Sometimes a drive cycle means that once the key is off the driver gets out and closes the door behind him and lets everything power down. I know it sounds silly but it really makes a difference in some modules so I just do it for all of them.

Z71Fan · August 19, 2008

I tried the new procedure this morning. I went out at 7:30 and took both fuses out. Two hours later I went back and put them in and started the truck. I let it run for 2 minutes without touching the temp controls and then turned it off and waited inside the truck. I then opened and closed the truck door (still waiting inside) and took the key out of the ignition. I waited for a minute and a half and then started the truck. The procedure still hasn't fixed the truck AC problems. Any other ideas?

Thanks,

Z71 Fan

Z71Fan · August 19, 2008

I tried the new procedure this morning. I went out at 7:30 and took both fuses out. Two hours later I went back and put them in and started the truck. I let it run for 2 minutes without touching the temp controls and then turned it off and waited inside the truck. I then opened and closed the truck door (still waiting inside) and took the key out of the ignition. I waited for a minute and a half and then started the truck. The procedure still hasn't fixed the truck AC problems. Any other ideas?

Thanks,

Z71 Fan

I have good news. After I reported a non-successful attempt this morning I then later went to run some errands. I can happily say that during the drive, maybe a couple of miles from the house, the AC vents on the driver side started blowing cold air! Maybe it just needed a little longer to get everything adjusted once the fuses were replaced and the truck was started. I would recommend taking a short drive afterward rather than thinking it will fix in a minute or so. All AC controls and vent speeds work as new.

My thanks to you sparkstech for continuing the thread last night and correctly pointing out that the second fuse also needed to be pulled.

I hope this helps somebody else out.

Thanks,

Z71 Fan

minibike132 · August 20, 2008

Glad you got it, this can be a pickey system and sometimes take alot to reset but like you said this all started with the battery so I was pretty confident this would get you fixed eventually. I've never had to do a roadtest after a learn but I'll give it a shot if one ever fails me.

coldbeer · December 10, 2008

BUMP -

great info! I'll try this again tonight, but with the door trick added in. I'll also remove the door panel fuse(didn't know to last time).

Here's my issue - AC works fine until I turn up the heat, then the heat is stuck. I have to stop the truck and let it sit and cool before the cool AC will blow again. There's also one very noticable flap/flop/bump in the dash, around the left side of the glove box a few seconds after I turn on the AC system.

History - I recently had the compressor and accumulator replaced b/c the air would only blow cool for 5-10 minutes before turning warm. The heat did not get stuck on until I replaced the parts listed above.

Domano 68 · August 19, 2009

I have a similar problem with my 03 1500HD. On hot days when I first start the truck, th AC blows warm air. After driving for a few min, sometimes several min, the AC starts to blow cold air. After reading this thread I recall that I replaced my battery a while back and the problem could have started at that time.

To make sure I understand the steps, the procedure is

Pull both fuses

Start truck and let run for 2 min

Exit truck (open and close door)

Replace fuses a few hours later

Start truck

Does anyone know if this fuse procedure will fix my problem?

TIA!

bill190 · August 19, 2009

This probably will solve the problem, and since it cropped up when replacing the battery, VERY probably!

As to the fuses, IF you know the correct fuses to pull, it would work.

Otherwise...

Disconnect the battery for 10 minutes, reconnect.

Turn ignition on without starting vehicle. Wait 1 minute.

DO NOT touch any A/C buttons during this minute!

Then start vehicle. Let idle for about 5 minutes.

Drive above 45 mph as soon as possible.

I call this "rebooting". Lots of things are computer controlled, so a "reboot" is worth a try.

FYI - It is best to start your own topic if a new problem (Click on NEWTOPIC) on the upper right). Don't worry about it this time...

Domano 68 · August 20, 2009

This probably will solve the problem, and since it cropped up when replacing the battery, VERY probably!

As to the fuses, IF you know the correct fuses to pull, it would work.

Otherwise...

Disconnect the battery for 10 minutes, reconnect.

Turn ignition on without starting vehicle. Wait 1 minute.

DO NOT touch any A/C buttons during this minute!

Then start vehicle. Let idle for about 5 minutes.

Drive above 45 mph as soon as possible.

I call this "rebooting". Lots of things are computer controlled, so a "reboot" is worth a try.

FYI - It is best to start your own topic if a new problem (Click on NEWTOPIC) on the upper right). Don't worry about it this time...

Great stuff, thanks much!!

jesteronyer6 · September 27, 2009

This probably will solve the problem, and since it cropped up when replacing the battery, VERY probably!

As to the fuses, IF you know the correct fuses to pull, it would work.

Otherwise...

Disconnect the battery for 10 minutes, reconnect.

Turn ignition on without starting vehicle. Wait 1 minute.

DO NOT touch any A/C buttons during this minute!

Then start vehicle. Let idle for about 5 minutes.

Drive above 45 mph as soon as possible.

I call this "rebooting". Lots of things are computer controlled, so a "reboot" is worth a try.

FYI - It is best to start your own topic if a new problem (Click on NEWTOPIC) on the upper right). Don't worry about it this time...

Should the A/C be set to off while doing all this or shoould it be set to defrost since in my case the vent mode is stuck in defrost?

gmtech121 · July 6, 2010

The actuator relearn is automatically done after a power loss. It takes about 30 seconds. A failed actuator feedback circuit which causes the counts to fluctuate during the reset is the main issue. It's not uncommon. You'll likely be replacing actuators eventually. There are software updates for door overruns as well caused by the flexing of the doors and the counts going below 0 or above 255 during the reset.