Fix buzzing sound coming from rear HVAC system on 2011 - 2017 Honda Odyssey (4th Gen)

UPDATE 2: So, I replaced the mode door actuator with one that I bought off Amazon for 1/5 the price of the OEM part 😆

I tested the original actuator and noticed that it was trying to go into a position that was not possible:

In other words, it wanted to rotate more than 180°, whereas it's only meant to rotate about 75° or so. This would explain the buzzing sound, as the motor in the actuator would skip gears as it gets stuck.

I guess I didn't really repair the original actuator when I opened it to clean it. But now...

Everything is working perfectly, let's see how long it lasts. I'll let updating this description!

Also...

When I went in a second time to switch out the old actuator for a new actuator, I found that you didn't need to take apart the HVAC ducts like I did in the video!

Simply unbolt the whole unit from the vehicle wall via three bolts and that gives you enough room to work back there.

UPDATE: The buzzing sound came back the next day. I have a hunch that it's the actuator arm getting stuck in one position and being unable to move from that position.

I will have to put something there to block it from going to the most closed position and hopefully it doesn't get stuck again.

I'll update once I do that!

Original description:

In this video, I document how I fix a buzzing sound coming from the rear heating/cooling system on my 2015 Honda Odyssey (fourth generation).

The buzzing sound is caused by the upper "mode door" motor (actuator motor) not being able to turn for some reason. The upper door is called the mode door and it selects between blowing air to the vents under the third row or to the vents in the ceiling.

(The lower door is called the "blend door" and it mixes cold air and hot air to give the desired temperature - that one is working perfectly in the video.)

Getting out the mode door actuator, taking it apart and cleaning the metal contacts on the biggest gear and cleaning the metal contacts make it work perfectly again (or so I thought)!

You can also buy a new actuator motor and simply replace it, which might be preferable. I actually broke all the plastic tabs off the unit when I was taking it apart, but luckily I bought a plastic welding gun a few days ago.

So, it's basically not necessary to remove the AC lines as the Honda service manual instructs! If you've got big hands, however, you may have to find some help (·•᷄‎ࡇ•᷅ )

Now, the heat and cold work at the back! Cold air comes from the vents on the roof and hot air comes from a vent under the third row seats.