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HVAC mode actuator not working properly

Tiny
ZPRIME7
  • MEMBER
  • 2005 CHEVROLET SILVERADO
  • 318,000 MILES
My mode actuator will not move when hooked up to wiring harness in the truck. I have removed the actuator and hooked it up to a 9 volt battery. I was able to move it in either direction.

As far as I know the actuator itself works. I can’t figure out why it won’t move when I try to control it with the HVAC head unit. All other functions work including heat/AC and fan speed.

My thought is that there may be a loose connection somewhere or the HVAC head unit is not sending correct signal to the mode actuator. What should the readings be on this harness from a multi meter? Any idea on which direction I should go from here?
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Monday, September 20th, 2021 AT 2:09 PM

33 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

There could be an issue with the power supply, a wiring issue, or even a ground issue.

Below, I attached a pic from the wiring schematic specific to the mode door. Check the voltage signals indicated. Also, confirm there is ground as well.

Let me know what you find or if you have other questions. Also, here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find.

Take care,

Joe

See pic below.

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Monday, September 20th, 2021 AT 5:45 PM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
I checked the voltage of each pin:
5: 4.72
6: 0
7: 3.40
8: â€
9: 0
10:.89

After this I checked the resistance from the pin that connects to the mode actuator to the pin the plugs into the back of the control module. Pins 6 and 9 both showed 0.4 for resistance (which is acceptable as far as I know). I’m not really sure what to make of this. I’d appreciate it if you could point me in a direction to go next.
Thank you.
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Tuesday, September 21st, 2021 AT 5:03 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

The voltage is too low. Pin 10 should have a 5v reference. You indicated it is.89v. Trace the wire (pin 10) and inspect it for damage, corrosion, or a short to ground.

Let me know what you find or if you have other questions.

Take care,

Joe
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Tuesday, September 21st, 2021 AT 6:36 PM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
So I made some more progress but still not there...

I checked the resistance on pin 10 and it was something well over 1. I just replaced the wire and now have resistance of.04. However the voltage has not changed it is sitting at.94 volts now. I used a slightly larger gauge wire than the one that was already wired into the harness since that’s what I had at the house. Not sure where to go from here. Thank you for the help so far!
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Wednesday, September 22nd, 2021 AT 2:21 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

I attached the wiring schematic below for the system. I highlighted several wires that are relevant for you.

Now, since the temperature actuators are working, we are getting power to the instrument junction box. Since you are still only getting.94v at the light blue/black wire, the issue is likely at the junction.

If you look at the last pic below, I have an arrow showing how power gets to pin 10. If this is the one you replaced, go back to the junction box and see if there is power there.

The problem seems to be from pin 10 voltage.

Let me know what you find.

Joe

See pics below.
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Wednesday, September 22nd, 2021 AT 3:35 PM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
Hey Joe,

Sorry for the delay. What/where would I find the junction box you are referring to here?
Thanks!
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Thursday, September 30th, 2021 AT 11:52 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

It's at the end of the dash on the right side. See pic 1 below.

Let me know if you find it.

Take care,

Joe

See pic below.
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Thursday, September 30th, 2021 AT 6:26 PM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
I located to junction box and found the blue/black wire that matches the one I cut and replaced behind the HVAC module. I am not getting any power from the wire at the junction box (first picture). Other wires are getting power at the junction box.

I am also assuming that the wire I cut behind the module will need to be spliced back in to provide the power? This can be seen in the second picture.
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Monday, October 4th, 2021 AT 8:13 AM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
The connector block that plugs in on the other side of the target wire has power everywhere except for the three wires circled. One is purple/white, and the others are the main black and red ones.
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Monday, October 4th, 2021 AT 8:41 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
The blue wire with the black tracer (the one you repaired) should provide a 5v reference. The idea you have no power is causing the mode door issue.

You need to go to the HVAC control module and check for a 5v reference right at the module. If there isn't one, chances are the module is bad.

I attached a pic below showing what and where to check. The idea that this wire has already been fixed indicates there could be an issue with the wire and not the module. That's why I'm recommending checking right at the module.

Let me know.

Joe
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Monday, October 4th, 2021 AT 7:06 PM
Tiny
ZPRIME7
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  • 18 POSTS
All right so I made some progress. There was 5volts at the module. I realized that I had cut the wire that ran to the junction out of the equation when I replaced the wire from the module. With the 3 loose ends spliced together I now have power to the mode actuator.

Only issue is that when I turn the key the actuator puts itself in the position shown in the image. After it moves to this position, I can’t get it to move anywhere else using the buttons on the module. I have reset it with a 9V battery but each time I plug it in it goes to this position and freezes.
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Wednesday, October 6th, 2021 AT 4:10 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Does it move when it's not attached or connected to the mode door?

Let me know.

Joe
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Wednesday, October 6th, 2021 AT 7:32 PM
Tiny
ZPRIME7
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  • 18 POSTS
I haven’t fully installed it. I just had it sitting on the floorboard next to the gas pedal. Plugged it into the harness and tried different functions and it wouldn’t move.
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Thursday, October 7th, 2021 AT 2:55 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Okay, if it isn't installed yet, let's try something. Disconnect the connector on the actuator. Next, check for power signals on the brown wire and the tan wires while changing the mode switch.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Also, make sure fuse HVAC 1 in the under-hood fuse box is good.

Let me know,

Joe
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Thursday, October 7th, 2021 AT 2:37 PM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
The HVAC fuse is good. The brown wire had a constant reading of 12V, and the tan wire had a reading of 2.5V. The voltages did not change when I cycled through different modes using the mode switch in the HVAC module.
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Friday, October 8th, 2021 AT 7:26 AM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
The yellow and green wire were showing about.02V and did not change when I cycled through modes. The blue wire is still holding its 5V ref.
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Friday, October 8th, 2021 AT 7:29 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

When you checked it, did you use the green and yellow wires as a ground?

Joe
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Friday, October 8th, 2021 AT 5:28 PM
Tiny
ZPRIME7
  • MEMBER
  • 18 POSTS
Originally no, I did not use the green and yellow wires as ground. I just checked again using these wires and the readings were the same and there was no change in voltage when I changed the mode. The only thing that was notable was the voltage was slightly lower (about.05V) when using the green wire as the ground.
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Tuesday, October 12th, 2021 AT 8:06 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
The voltage should be changing. I'm questioning if the HVAC controller is bad. Are you able to test the same wires right at the controller? Or maybe you already have. I'm suggesting this because if the fuse is good, there is battery voltage to the controller, but it doesn't respond, the controller itself must be bad.

Let me know.

Joe
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Tuesday, October 12th, 2021 AT 5:30 PM
Tiny
ZPRIME7
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  • 18 POSTS
I just tested the wires right at the controller and got the same results. Also, just to confirm you are referring to the 10-amp HVAC/ECAS fuse under the hood correct?
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Wednesday, October 13th, 2021 AT 9:02 AM

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