2009 Tundra CrewMax SR5-HVAC Gears Popping

Hi guys.

This issue started about a year ago. The best I recall, once I turned my truck off, I began to hear repetitive popping (like plastic gears slipping) from the servo area. That sound eventually went away, and I lost AC in my dash vents.

Starting at that time, I turn the truck off, and I can hear the servo (and maybe other HVAC gears) slowly seeking a resting position and cycling back, and then forth. And then turning back, and then forth again. The cycle repeats itself about 5-6 times over the time span of about 1 min. before coming to a rest.

I have ac/heat coming out of the defrost. I have residual air/heat coming out of the floor and vents. When selecting through the cabin air cycles, I hear a drop in the defrost pressure, but not a noticeable difference in the remaining air ports like vents and floor.

I replaced the entire servo unit part number 87106-0C070.

Before reassembling the unit, I plugged the two plugs in to observe the operation of the servo unit gears. They over rotated and the result was one slipping out of position (big tooth in small slot) . I popped the gear out and realigned, reassembled, and installed. My hopes were, once installed, the slots, arms, and receiving HVAC system, would limit the servo gears and prevent them from over rotating.

That's not been the case. I'm back to my original issue. Being somewhat familiar with diesel mechanics and troubleshooting, it makes me think there's a sending unit failure or limiting sensor or wire failure maybe? I say that because it did this over-rotation thing while the servo and the HVAC receiving unit were NOT married together, which is what I think I'm hearing now that its assembled. Preinstall. Confused? Me too.

 

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