Hvac blend door issue, sound behind dash

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Hvac blend door issue, sound behind dash

Postby bigBADbenny » Sat Mar 07, 2020 8:45 am

Hvac blend door actuators.

Symptoms: bubbling, murmuring, buzzing, sound, noise behind dash on startup, after key off, often mistaken for improper coolant system bleed, air pocket in heater core.

The difference being the noise happens on key on, and after key off.

There’s two actuators on the rhs of the passenger footwell, on the hvac airbox which contains the heater core, ac condenser and the blend doors that actuate when the mode button is cycled.

Two potential issues:
The tab on the blend door motor has popped out of the track/cam that moves the blend door: reseat it and test the mode button.

Or the motors position sensing is worn out.

Carefully remove the motor, replace it with a working item new or s/h.

Or open the motors gear case. Slightly bend the actuator position sensing fingers inside to fresh track.

Add some quality, plastic friendly grease, probably silicone grease or food grade grease.

Reseal and reinstall the blend door motor and test using the mode button.

Iirc I tested it before I replaced all of the trim, just to be sure.

Iirc this can be a dash out procedure on LHD cars, but always consult the FSM regardless.

Link from the forum first hit:
https://www.google.com.au/search?biw=49 ... 1vrDUmz7z4


Here’s a pic from when I did mine.
viewtopic.php?f=10&t=20939&p=356707&hilit=fixed#p356707

Here’s the FSM workshop manual link on the forum for procedures:

FAQ: Subaru FSM Service Manual Parts Procedures Diagnostics • club.liberty.asn.au

viewtopic.php?f=6&t=34980

Tools: trim removal tools, a good 1/4” metric ratchet set with hex bits, sockets and extensions, phillips screw drivers in short and long.
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Re: Hvac blend door issue, sound behind dash

Postby Kimmo » Sun Mar 07, 2021 3:11 pm

So yeah, mine was making the stupid noise and pointing the air at random, had a go at this.

Here's a rundown for what trim needs to be removed:

Lift up the front of the back half of the centre console. Pop out the gear lever surround (or whatever for autos), remove the silver trim and non-ashtray, then you can get the left side panel off the front half of the centre console.

Remove the dash side panel (where the passenger door closes up to the dash), and the bit of trim under the glovebox, which can then be removed. Or do this before the other part, doesn't matter.

Now it's all exposed; you just need to unplug the loom and you can get that bastard servo out. I didn't use a ratchet handle, just a stubby screwdriver, and it was doable but no fun. Reassembly even more so.


Anyway, once you've unscrewed the servo, best to plug it back in and test it to make sure its feedback has crapped out - maybe the followers just popped out of the cam. There's a little clip holding it onto the output shaft; careful when you remove it. Here's what you see when you crack it open.
hvac 1.jpg
hvac 1.jpg (118.92 KiB) Viewed 5788 times


My car has 180,000-odd on it, but my tracks were far from worn through. Plenty of spare grease inside the unit too - you can just reposition the old stuff instead of digging up more.
hvac 2.jpg
hvac 2.jpg (146.74 KiB) Viewed 5788 times


I figured the brushes were simply no longer pressing hard enough, so there was no need to bend them off track, just to tweak a bit of extra life back in.
hvac 3.jpg
hvac 3.jpg (119.62 KiB) Viewed 5788 times


Tested it, and sure enough, that did the trick.I got it into my head that the adjacent servo was also playing up (turns out it wasn't; I'd mistaken it for the fresh/recirc servo), and the above pic is from that one - for some reason it has more brushes. Anyway, when I tried to pry the arm off the output shaft, I discovered the hard way it was glued on. Fixed it by sacrificing a 7mm drillbit and slathering it in superglue.
hvac 4.jpg
hvac 4.jpg (135.62 KiB) Viewed 5788 times


Also, bonus discovery - another pair of mystery plugs, this time the same colour (unlike the pair inside the driver's kick panel). Anyone wanna hazard a guess what happens if you plug them together?
I wasn't game in case it initiated the self-destruct procedure or something...
hvac 5.jpg
hvac 5.jpg (150.93 KiB) Viewed 5788 times
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Re: Hvac blend door issue, sound behind dash

Postby bigBADbenny » Sat Mar 13, 2021 7:43 am

Excellent writeup and pics, thanks very much!

Yep it’s simply a second set of diagnostic test mode connectors, the other set is around the cabin fuse box area.
When one pair of connectors is temporarily plugged, eg the radiator fans will cycle etc.
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Re: Hvac blend door issue, sound behind dash

Postby tkdbboy » Fri Mar 22, 2024 1:31 pm

So this hellish process was done on PreFL 06 STI with 320k on it.
Last month the typewriter evolved into a loud whirring when starting and turning off the car , and cycling MODE. Fair to say, very annoying.

Consulted the brains trust aka BigBadBenny as he's gone through hell and back before.

Got to the two actuators in the footwell and saw the noise was coming from the top one which is related to Mode button. Below one is Temp Dial.
Opened the Mode Actuator and upon inspection, the fingers had actually worn through the black track completely that you could see the plastic underneath.
Tried to move the fingers a bit to the side, clean and grease but no dice. Problem still was there when the Mode track moved upwards.
This meant that maybe the motor had an issue, fingers weren't offset completely correctly or worse, there was extra resistance inside the HVAC unit causing the motor to struggle.
Decided to source a replacement as a comparison.

Part numbers:
72131AG190 - Original part number from checking online
72131AG370 - Substitution part no from Amayama
72131AG130 - Substitution part no from Partsouq

Quoted $275 from Subaru Frankston for 72131AG190.
Couldn't find a replacement on eBay ... other than Lithuania.

Hunted partout posts and found one from an 05 2.5NA. Assumed all PreFL are the same. Turns out the 05 2.5NA Mode is the same as the Temp one. Mine are different so the plugs didn't match.
Sourced an 05 GT Spec B Mode one which Denso Part Number and Plug type aligned for $50.

To my luck, inside track was mint, so gave it a clean an applied ChemLube Silicone Grease.
Installed the Actuator and tested mode. Silent bliss. Cheers again to Ben for reliving the horrors of this process!

Denso part numbers below:

2007 GT Spec B
Mode 063700-8610
Temp 063700-8630

2006 STI
Mode 063700-8610
Temp 113800-2320

2005 GT Spec B
Mode 063700-8610
Temp 113800-2320

2005 2.5NA
Mode 113800-2320
Temp 113800-2320

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