Rear Blend Door calibration - Tech II

JayArr

Original poster
Member
Sep 24, 2018
504
Mission BC Canada
Hi All

When I use my Tech II I can calibrate the blend door motor, when I run the calibration I can hear motors in the dash turning and moving.

Can anyone confirm that the two actuator motors in the rear are also turning and calibrating?

Is this a one shot deal where all 5 of them recalibrate or is it front only and there no software routine for the rear motors?

I've got no heat in the back but the fan runs fine so I'm thinking a door isn't where it needs to be. I've ordered a new door motor but if I can calibrate the one that is there I can save $80.

JayArr
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
AFAIK, it calibrates the rear each time the truck is started because when I had a failed actuator, every time I started the truck, it would do the ticking noise.

Have you tried to just pull the HVAC B fuse to do the calibration? You ever hear anything from back there? I know I let mine tick like that until it eventually stopped, probably after the gears were completely destroyed.

Another possibility is that the diverter valve is stuck closed and not letting coolant flow to the rear heater core. Check the hoses just behind the right rear wheel if they get warm.
 

JayArr

Original poster
Member
Sep 24, 2018
504
Mission BC Canada
Now that you mention it there was a clicking noise back there when I first bought the truck but it went away. Now I'm thinking I've done the same thing as you, I've let the gears strip. There were so many other things to do when I first got it that a noise from the rear inside didn't rate attention, I was changing the engine and rebuilding big greasy parts. LOL

I guess I'll pull it in the morning and see what's left of the gears, I have one on order that should arrive Monday.
 
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mrrsm

Lifetime VIP Donor
Supporting Donor
Member
Oct 22, 2015
7,641
Tampa Bay Area
This GMTN Rear HVAC Module and Blower Motor R&R Thread may prove interesting...


...and there MAY be some Additional Steps to cover that specific set of Blend Door Activation & Blower Motor Testing set forth in this Official GM TECH2 ASE Procedural "Bible", too:
 

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flyboy2610

Member
Aug 24, 2021
460
Lincoln, Ne.
Be real careful when removing the blend door actuator from that rear blend door! I had to do mine (same ticking noise) and even though I was trying to carefully slide it off the shaft, the shaft on the blend door still broke!
D'oh!.jpg

I couldn't find a new door anywhere so I got one from the local automotive recycling facility. They are a pain in the you know what to replace!
No more ticking noise, though!
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Even though I replaced the rear heater core when I first got my EXT, all the actuators broke and never bothered to fix it again. Didn't miss it nor the rear A/C.
 

JayArr

Original poster
Member
Sep 24, 2018
504
Mission BC Canada
I have a 155 pound Golden Retriever that lives back there. All the rear seats have been removed and plywood was installed to make the floor flat and level. Then we installed 4" foam and blankets. We used to have two furry beasts (and will again) so that's their space when we go travelling with the trailer. They need the heating and air con to work properly.
 

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flyboy2610

Member
Aug 24, 2021
460
Lincoln, Ne.
Sorry to hear of the loss of your companion! Heat and AC will definitely make the canines happier!
 

Mektek

Member
May 2, 2017
656
FL
The actuators are calibrated only once one upon initial power up of the climate control module and remain that way as long as the calibration data is valid. Each actuator has an internal feedback loop that maintains the set position.
The clicking is from a cracked gear or a failure of the components that operate the feedback loop within the actuator. The actuator will keep trying to move to reach the desired value - with defective components that may never succeed.
 

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