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If you haven’t already, try removing the actuator and rotate the door manually using the stub of the shaft. If it feels like the door is moving with it, turn the key on, set blower to speed 1 or 2 and see if it changes to defrost/panel/floor as you manually rotate the door.
What you need to focus on is the mode door actuator and door, located on the left end of the HVAC housing. You should be able to see it from the driver foot well, though removing the trim panel from under the dash might be necessary to replace it.
If you’re only getting air from the defrost then most likely the actuator has failed, however it’s also possible the door is jammed or broken (or both).
With the key on, watch the position indicator on the actuator - if it’s not rotating while selecting modes, verifying the power, ground and control feeds to the actuator are the next step.
If it’s humming like it’s trying to rotate but there’s no movement, the internal gears of the actuator have stripped and it requires replacement.
If it is rotating but the mode isn’t changing, remove the actuator and try to move the door by hand using the splines for the actuator - you’ll know if the door’s in tact because there’s a certain weight/feel to it. If it’s broken (specifically the shaft) it will be very easy to turn.
If the door is jammed, you may be able to free it depending on the obstruction. If it’s broken, the whole HVAC housing needs to be removed in order for the door to be replaced.
The HVAC housing is illustrated below. I did a write up on HVAC actuators a while back that will provide more in-depth info if you’re curious.
The mode door actuator on my 95 k1500 doesn’t seem to have any power going to it. AC control panel and actuator replaced but it still makes no sound and doesn’t move. Any direction on running new wiring for that actuator or another next step?
Thanks for your reply. Due to my physical size, I was unable to get below my AC housing and see the linkage on the actuator. Too fat... A friend assisted me, and we were able to replace the linkage, which over the years had broken.
The mode door actuator on my 95 k1500 doesn’t seem to have any power going to it. AC control panel and actuator replaced but it still makes no sound and doesn’t move. Any direction on running new wiring for that actuator or another next step?
Are the other 2 actuators (temp blend and recirc) working?
Have you verified if it has power and ground using a test light or meter?
The actuators all receive power from the heater/ac fuse in the cabin fuse block. They all share the same ground circuit at point G120 at the rear of the right cylinder head.
If the other 2 actuators are working, the problem is narrowed down to one of the splices in the power/ground circuits or the control circuit.
Disconnect the mode door actuator plug. With the key on, connect a test light between the brown and black wires - it should light. If not, use independent power and ground sources to check the circuits.
If the power and ground circuits are functional, set the blower motor to low and connect a voltmeter to the white wire and ground. While slowly turning the mode door control **** back and forth, watch for a steady, consistent change in voltage. If it’s not there, remove the HVAC control panel and monitor the voltage at the back of the panel while back probing the connector - if it’s changing, run a new control wire between the panel and actuator.
My ac on my 1994 c1500 was just blowing hot air. Read all kinds of links to blend door actuator repair. Sounded like a nightmare to me. Wanted to insure it was blend door actuator prior to removing anything at all so, I read your responses and great information you supplied. I wanted to insure power supply to actuator so I unplugged the electrical to the actuator, turned key on and check power incoming. During this time of checking control module kept flashing full bars. I had power to actuator. Connected plug back up and for whatever reason went thru warmer and colder settings and actually watched the actuator start to work properly. I’m wondering if I stumbled on to an easy reset to control module. Everything working fine and didn’t have to take out suggested nightmare on lower right side under fan.
My ac on my 1994 c1500 was just blowing hot air. Read all kinds of links to blend door actuator repair. Sounded like a nightmare to me. Wanted to insure it was blend door actuator prior to removing anything at all so, I read your responses and great information you supplied. I wanted to insure power supply to actuator so I unplugged the electrical to the actuator, turned key on and check power incoming. During this time of checking control module kept flashing full bars. I had power to actuator. Connected plug back up and for whatever reason went thru warmer and colder settings and actually watched the actuator start to work properly. I’m wondering if I stumbled on to an easy reset to control module. Everything working fine and didn’t have to take out suggested nightmare on lower right side under fan.
I’m glad this was helpful to you and thanks for taking time to actually read the thread instead of responding just because the title matched your issues.
Just a guess, since I don’t know the actual process off the top of my head, but you probably triggered a calibration.
Electronic actuators and controllers can be “quirky” like that. I‘ve solved many HVAC concerns by initiating a calibration, with or without a scan tool. I’ve never had the time to do in-depth testing & record the data, so I don’t know anything for sure, but the best I can conclude without more information is:
1) The contacts get worn, dirty and/or fretting corrosion within the normal range of use; particularly in actuators that have position feedback sensors. Leaving it on the same settings most of the time (which I do all the time but who cares? ) allows contamination to collect on the contacts. The calibration sweeps the door and actuator thru its full range of motion and that cleans the contacts well enough to restore normal operation.
A relatively recent development in manufacturing has been automated calibrations with key cycles. I don’t know for sure when this started but my 2015 Silverado and 2016 Grand Caravan both complete a calibration cycle within the first minute or so of startup. Other makes will run it within a few minutes of key off or engine shutdown. I suspect the internal contact cleaning from the calibrations is a fringe benefit of the process, as I’m sure it has more to do with the absolute madness of programming a data network to make an automobile more efficient.
But I digress…
2) Something electrically drains the power of the module just enough to somehow alter/corrupt/reset the module’s memory. At the next key cycle, it self-calibrates but the module is using an actuator’s last known position instead of one end of the range or the other. Thinking about it now, it’s also possible that any random position could be recorded as the stop point and it doesn’t necessarily have to be the actuator’s last known position.
Whatever the reason, the module now assumes that position is the end of its travel. The calibration is recorded incorrectly, the module realizes it just sh*t its pants, and everything about that actuator is put on hold until all the wiping is over (i.e. a calibration with a scan tool is performed or for pre-OBD2 vehicles, the right buttons on the controller are pressed and/or loss of power thru fuse pulling or battery disconnect).
I’ve no solid evidence of any of this being true, but it remains a hypothesis until it can be disproven using the scientific method or someone really important says it’s true. The latter will probably happen first….
As for your truck in particular - don’t be too surprised if the actuator fails again in the next few weeks or months. Calibrations sometimes only work for so long due to a list of factors I’m not willing to fat-finger my way through this damn phone keyboard to explain.
THX for explaining! I watched some disastrous videos on the net regarding the blend door actuator, just shook my head and said to myself, I don't think so. It was a cake walk to remove glove box and put test light on that plug in. So even if I have to replace in near future that is going to be a cake walk too.
September 3rd, 2021, 8:09 PM
) allows contamination to collect on the contacts. The calibration sweeps the door and actuator thru its full range of motion and that cleans the contacts well enough to restore normal operation.