The topic of how to perform the actuator recalibration procedure on Chevrolet , GMC and Cadillac Trucks and SUVs has become an ever increasing topic of discussion.
For manual systems it does not matter where the a/c controls are set but if you feel the need to do something, turn the blower switch on (I prefer speed 3) and set the temperature sliders about .5″ to .75″ from full cold.
For auto systems, press the auto button, with the key on.
Turn the ignition off.
Remove the HVAC/ECAS , 10 amp fuse in the underhood fuse box* or disconnect the battery for one minute.
*Fuse locations can vary from year to year and between different models. Hopefully I will be able to build a list for this.
Install the HVAC fuse or reconnect the battery.
Start the engine. On systems with auto a/c controls the controls will default to 74 degrees F when the ignition is turned back on.
DO NOT TOUCH the a/c controls.
Let the engine run for 1-2 minutes.
Turn the ignition off for at least 10 seconds but no more than 30 seconds.
Restart the engine and then test the a/c controls.
Question: I recently swapped out both of the rear HVAC actuators and resistor on my 2005 GMC Envoy XL and after the calibration process I noticed the air was not changing. I took it to a trusted mechanic and they tried swapping out all the actuators, resistor, rear HVAC control module, fuses, and nothing has worked. They checked inside the unit and they said the door is not obstructed but the door for the air temp is not fully rotating one way or the other, it is leaving a gap on either side which is why the air is mixing. They suggested taking it to a dealer to have the programming on it redone to see if that will fix the issue since everything is working fine except for the computer not closing the temp door fully one way or the other. What are your thoughts on this?
In order to help I have to have a better understanding of your situation. What was the original problem with you HVAC system and is it limited to the rear unit? Does your system have manual or auto controls? Is the problem present using both the front and rear control heads for the rear system? What brands of parts were used? Were they new or used parts? What exactly is the present complaint? Do you have access to scan tool that will communicate with the system? If so, do you know what the calibration file number is? You state that the air is mixing, what are the vent temperatures in various settings? What is the ambient temperature and humidity? I know these may seem like a lot of questions but without being able to physically interact with your Envoy, I need you to give me all of the information that I would be looking for if your GMC was in my shop.
Manual controls. Only rear HVAC. Actuator went bad so I figured I replace both and the resistor. The shop swapped it all parts and rear controls. Checked all fuses and scan tool to calibrate. Nothing worked. Parts work fine just for some reason the temp door won’t fully rotate. No blockage. Just seems like the computer will not move the temp door all the way. No codes. Weird even the shop said so.
My recommendation is to do a recalibration of the rear system. To do this first set the front blower switch for the rear HVAC system to rear control. Next remove the HVAC B fuse in the rear fuse box for a minimum of 10 seconds. Install the HVAC B fuse and turn the ignition on. Wait for at least 40 seconds (I prefer a full minute or more until I hear/see no more movement in the system). Turn the ignition off for at least ten seconds before restarting the engine and checking the system. Do Not touch any controls during the recalibration process. You may need to try is several times in order for it to take. If it still does not make a difference swap the two rear actuators and see if the problem moves with the actuator. One last thing I wanted to ask. Are you experiencing a temperature problem with the rear system or is it a problem with visually not seeing the full movement?
I have a 2005 GMC Envoy XL, today I took out my climate control module (manual controls) to replace some burnt out bulbs. Afterwards I put the module back in and a while later on the way to the store I noticed the air was hot although the setting was on cool and the AC buttons would not work and the vents would not change although I did have control over the fan speeds. I pulled all of the HVAC fuses under the left middle seat and that did not work. Then I disconnected the battery, reconnected the battery, and pulled the ECAS fuse (didn’t see a HVAC/ECAS fuse) from under the hood and that did not work. I am very careful in my work and I can solder very well so I know I did not harm the module so what do you think I can do?
On that vehicle the HVAC B fuse in the rear seat fuse box is the one that would have to be pulled to start the recalibration procedure. Reinstalling a disconnected HVAC control head will do the same thing because continuous battery power has been removed and resupplied. So we basically have three scenarios to look at. 1. Were the controls touched during the recalibration process? Interrupting the process leaves the system stuck in whatever place it was at when the interruption occurred. 2. There is a faulty actuator that has stuck and interrupted the recalibration process and left the system stuck. Most of the time it is the mode actuator at fault. Without a capable scan tool the option is to locate each actuator and observe them one at a time under repeated recalibrations to see which one is stuck or stick and which one happens first. 3. Something went wrong during the bulb replacement. Could be a loose terminal in the harness connector or something else internal.
Yeah I pulled the HVAC B and never touched the controls and it won’t even go through the calibration process like it did a few months ago when I changed the rear blend door actuator. When I first took the climate control module out I could hear the actuators move. I’m just stumped right now and my trusted mechanic is out until the 5th lol lucky me.
I’m having a problem with the rear HVAC on a 2004 Chevrolet Tahoe LT. I started with both mode and temperature controls failing. It was stuck in upper mode (ceiling vents) and cold temperature.
I replaced both blend door actuators and the rear control module. Now mode works properly but temperature is still stuck in cold.
During the recalibration procedure, I can see the temperature actuator move, starting from cold it goes all the way to hot, then back to cold. However after calibration is complete, adjusting the temperature control has no effect.
Also, the temperature actuator moves from cold to hot to cold every time the ignition is turned on, not just after removing HVAC/ECAS fuse.
The controls are full automatic, control of the rear can be done at the front ceiling or set to aux where the controls are at the rear of the center console (for rear passenger access). I have tried recalibrate with the control set to off and in auto mode both, not sure that matters though just as long as the controls aren’t touched during recalibrate.
Appreciate any ideas if you have them, other than the one I’m leaning towards, button it up and sell it 🙂
This system really needs to be diagnosed with a capable scan tool. With that said there may be a few things that we can check. Number one what are the part numbers of the installed parts? You stated that you replaced the rear control module. Was that located near the auxiliary mode actuator? Was it a new part or used? Do you have or have access to a capable scan tool? How about a multimeter?
The rear control module is AC Delco 15-73506 (OEM 15832319). It’s located roughly between the auxiliary mode and temperature actuators, bolted to the auxiliary heater core housing. The actuators are both Dorman 604-111 (OEM 89018375). All parts are new.
I don’t have a scan tool but do have a multi-meter. Based on another one of your articles I did some probing of the voltages at the electrical connector to the temp actuator. There are 5 wires on the connector, from left to right they are gray, blue, yellow, white and brown.
Brown is +12v, white appears to be chassis ground while yellow appears to be another ground.
Gray is +5v at the beginning of the calibration. It then goes to 0 while the actuator turns counter-clockwise, then to +5 while the actuator turns clockwise, then to +2.5v and it stays there. It calibrates every time the vehicle is started regardless of whether power is removed between starts or not.
Blue varies between 0 to +5v with the variance apparently relative to the position of the actuator. It starts at +5, then gradually goes to 0 as the actuator turns counter-clockwise, then gradually returns to +5 as the actuator turns clockwise.
All voltages are with the vehicle running using white as ground.
Well it’s working now. I did one thing different and I’m not sure if it’s relevant. I left the vehicle battery disconnected for ~45 min.
In all my testing, I noticed my battery was 4 years old and I follow a personal philosophy to change automotive batteries every 4 years. So I took the battery out, went to the store and bought another one.
After installing the battery, the aux temp actuator calibration behaved differently. It went all the way counter-clockwise as usual, then as it started turning clockwise, it did so in steps, perhaps 5 degrees at a time with a short pause in between steps. After it was done, I adjusted the temperature control and the actuator obeyed.
Could it need more than a minute without power? Every time I ran the recalibrate I set a timer, the power was removed for at least 1 min 15 seconds each time. I also was disconnecting the vehicle battery, not pulling the fuse. I did pull the fuse a couple times and observed that the mode actuator didn’t recalibrate…raising some suspicions that pulling HVAC/ECAS wasn’t enough. This is only my observation, take it for what it’s worth — likely nothing.
Hopefully this is resolved. Thanks for your thoughtful consideration of my problem.
My guess would be that you were experiencing “logic lock”. It is becoming more common and basically the computers brains get scrambled and you have to discharge current from all modules to clear it out. We do it by quicker by disconnecting both battery cables from the battery and holding the two cable ends together for about one minute. You can also just disconnect the negative battery terminal and turn on a non computer controlled load for the same amount of time. This is getting harder because there are very few things outside of that criteria anymore.
Also in an earlier reply to you I mentioned that removing the HVAC/ECAS fuse will not recalibrate the rear HVAC system. GM in their service information does not list a procedure for performing a recalibration on the rear system. However following other systems design and logic, one would need to remove the ECC fuse from the interior fuse box to try.
I am also a fan of replacing batteries every 4 years regardless of condition. A few years back a national study found that the average battery life was 39 months. That was taking all grades and manufacturers into account.
Brown should be battery voltage with the ignition on.
Gray should be 5 volt reference with the ignition on.
Yellow is return ground. Similar to chassis ground but technically different.
Dark Blue is the sensor position signal and should vary between 0 and 5 volts.
White/Black is the command wire and should be 0, 2.5 or 5 volts depending on the command signal from the module.
All readings should be checked against a known good chassis ground.
If you still have the old parts check to see if the numbers on the actuators are the same or not?
GM Service Information does not state if the rear system needs a recalibration procedure or not when parts are changed. However if it were to be done the ECC fuse in the interior fuse box would be the one that would have to be removed in order to initialize the recalibration.
I have an 2008 Chevy Trailblazer SS. I am going to try and see if this fixes my issue of cool air blowing out of the vents. The passenger side is blowing out cool but not cold air and the driver side is blowing out a warm cool air. It’s not even close to being cold. I am told it might be a motorized blend door issue behind the dash board. Your thoughts?
From your description it sounds more like a low refrigerant charge. If the vent temperature will get dramatically hotter when you change the temperature setting to full hot, concentrate on refrigerant level and not actuators.
Hi Sparky
Both processes don’t work for a 2013 Chevy Captiva. I tried the “remove XM/HVAC fuse” method. I tried “remove battery cable” method. It appears both are ineffective.
My Air Conditioner Control stays lit up for about 2-3 seconds then goes off for 1-3 seconds. The blower keep blowing continuously but AC toggles from being ON then OFF – so intermittent cool air.
I recently used a “recharge” can. The following directions precisely; however a little AC coolant spurt out. Perhaps that is what has tripped the system – assuming a DTC stands in the way of a continuous blast of cool air.
What do you suggest?
GM service information only states a procedure using a scan tool for your vehicle actuators to be recalibrated. If it can be done by removing a fuse I would recommend trying the RVS/HVAC/DLC fuse in the interior fuse box. If your a/c display goes blank, more than likely you will have a faulty HVAC control head assembly or there is a problem on a communication line to it.
I also have a 2008 Trailblazer. I have run through the re-calibration procedure several times, but I continue to have cold air come out of the passenger side vents and warm air come out of the driver’s side vents when full cold is set for both. It doesn’t have a HVAC fuse, so I disconnected the battery positive post for about 15 mins. Does this mean I wil have to change the blend door on the driver side?
Most likely you will need to replace the driver’s temperature/blend door actuator. There are few things you need to think about first though. Does the driver’s side vents get substantially warmer when you change the setting to heat? When the system is on full cold are you getting 45 F vent temperature on both passenger side vents? Or is the far right one cold and all vents get slightly warmer than the previous vent as you move to the left?
Sparky:
I gotta give credit where credit is due. Your procedure works like a champ! I have a 2004 Avalanche and this was the easiest 5 minute fix I have found for my truck. Thanks.
Electrical problems never cease to amaze nor stump me. My AC system was working fine on the highway driving home from the airport when is decided to go FULL HOT when it was only 83 degrees outside. The truck sat baking in the July Florida sun for the 4 days previous and had it’s share of summer thunderstorms as well. Still, I had no warning that there was any problem looming until it just happened.