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In this video I have a look at an older GMC Sierra that had a customer complaint of the HVAC being stuck on defrost. My gut told me "prolly just a bad actuator." However, the data showed us something different.
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49 thoughts on “Gmc sierra: stuck on defrost”
  1. Avataaar/Circle Created with python_avatars Basically Anything says:

    I love you now

  2. Avataaar/Circle Created with python_avatars beastumfan says:

    Could you recalibrate?

  3. Avataaar/Circle Created with python_avatars Trulyblessedziiz says:

    Eric, you are the man brother 🙌

  4. Avataaar/Circle Created with python_avatars Michael Long says:


  5. Avataaar/Circle Created with python_avatars Michael Long says:

    I want to thank you for such a great review of this issue. I have been trouble shooting this same issue on a 2002 2500HD for a month. I replaced the actuator for the same failure and had no change. Still stuck when switched to defrost.
    After watching your video, I went back and checked signal voltage again with the same 5v shut off at defrost. Added the screw to motor housing and it works perfect.
    Who would have thought that foam seal could cause this much of a problem. Thanks again.

  6. Avataaar/Circle Created with python_avatars Ben Brueggeman says:

    Thanks. Helped out a lot. Have the same problem on an 02 silverado

  7. Avataaar/Circle Created with python_avatars John Bair, D.C. says:

    Genius fix! Thanks

  8. Avataaar/Circle Created with python_avatars Tyler Morin says:

    Nice job…I feel much more informed now..good Ole technical know how

  9. Avataaar/Circle Created with python_avatars William Icard says:

    Great video brother going through the same deal was suspected it bit you verified thanks a bunch

  10. Avataaar/Circle Created with python_avatars stan sheldon says:

    Thank you, This problem just started on my 2001 Chevy Silverado. granted I don't have any foam dust but at least you gave me some ideas where to look.

  11. Avataaar/Circle Created with python_avatars N Trails says:

    I'm hoping that customer decides to continue fixing the HVAC on his 2001 GM 1500, I have the same model year and have yet another non-straightforward repair needs with mine. Mine is actually in the recirq actuator, which you touched upon it wasn't showing the proper functionality, but never went any further into it. Mine, I have gone all the way up in there, changed out that actuator, only to have it exhibit WORSE functionality… it opens the door when commanded to close it, and vice versa… it also commands the compressor to run when recirq is commanded, but the door is closed. I opened up the old actuator and found a split nylon drive gear, which I was able to rotate 180 degrees so the damaged teeth won't be in contact with the other gears. Now I've just gotta totally tear apart the dash again (including cutting through the far right side panel duct, which it only taped back together now with foil backed duct tape) and swap this repaired OEM actuator back up in there.
    I find myself watching at least one if ur videos most every day! I've been subscribed for over 6 months now and still I find you keep it interesting, at least enough to keep my interest. If I wasn't all the way out here in SF I'd for sure pop in ur shop fora chat… Who knows when I might be back there upstate way! BTW… my daughter spent 4 years at Marist in Poughkeepsie back in the 2012-2016 timeframe… If I knew about y'all back then that would've been the chance to visit, huh?

  12. Avataaar/Circle Created with python_avatars jewllake says:

    I came back to comment, that now, on my 2006 GMC yukon the recirculation door was stuck on fresh air only. I was able to pull the digitial climate control brain out and ground the low reference yellow wire and with the ignition in the "run" position I gott the door to move to recirculation. Then through the blower motor access hole I was able to glue new weather stripping to the door so it no longer overtraveled and now it works like it should. Even if the foam does not deteriorate what ends up happening is that it looses it's memory and stays compressed thus allowing the door to move too far – stupid design!

  13. Avataaar/Circle Created with python_avatars Ml M says:

    EXCELLENT VIDEO, EXPLANATION, CLARITY. you are awesome buddy
    thanks for sharing

  14. Avataaar/Circle Created with python_avatars Chris Steele says:

    Hey everyone Also sometimes I share this, the Bible says that GOD loves us so much that he sent his son JESUS CHRIST to this earth and HE lived a perfect sinless life.And JESUS went to a cross and gave HIS life for us.And rose again in 3 days and who ever will receive JESUS AS THEIR SAVIOR AND ASK HIM TO COME INTO THEIR HEART AND FORGIVE THEIR SINS,HE WILL TAKE YOU TO HEAVEN.

  15. Avataaar/Circle Created with python_avatars James Hardeman says:

    My son has a diesel truck with small electric vacuum pump for heater control and at runs constant. He has replaced 3 times because it burns up.

  16. Avataaar/Circle Created with python_avatars Jeffery Murphy says:

    Great job , mines keep going out in defrost mode 40 year diesel technician, replaced twice but in the morning going to jump reverse wire remove in install 3/32 dowel pin thanks

  17. Avataaar/Circle Created with python_avatars Faul Durand says:

    Love the video. Simple, honest and, funny.

  18. Avataaar/Circle Created with python_avatars Ethan Beveridge says:

    Thanks to this video I got my truck fixed because it was doing literally the same exact thing as this truck I tried everything but once I watched this video I knew exactly what was wrong and how to fix it I had the same intentions to what you had when you were diagnosing this truck I’m glad you made a video about this because no one else did

  19. Avataaar/Circle Created with python_avatars Ronald Carrel says:

    Blend doors suck, especially since they make them virtually untouchable in most vehicles without tearing the whole dash apart.

  20. Avataaar/Circle Created with python_avatars Ronald Carrel says:

    Excellent video!
    I applaud your skills!
    Unbelievable detective work!

    You should change the name of your channel to “The Educated Mechanic”.

    Plus, plus, you even speak your native tongue correctly – see, saw, seen, does, don’t, doesn’t, very unusual in todays sloppy world.

    Thank you for your efforts and your ability to show how you research different problems.


  21. Avataaar/Circle Created with python_avatars John Adams says:

    Great detective work Eric. Outstanding. Keep those videos rolling.

  22. Avataaar/Circle Created with python_avatars Gary Meredith says:

    As usual Eric you are a source of Education on these blend door's for the AC and heater systems unlike the old cables .

  23. Avataaar/Circle Created with python_avatars Terry Peters says:

    I will be watching for foam up on the dash of my Tahoe, thanks.

  24. Avataaar/Circle Created with python_avatars WTF TOOLS says:

    there is a RESET process for GM trucks to learn the blend door open and closed limits.

  25. Avataaar/Circle Created with python_avatars Mike Durnell says:

    Hemc Eric

  26. Avataaar/Circle Created with python_avatars James Field says:

    New York miles and Arizona miles are two different things. The foam fell apart not the frame and body

  27. Avataaar/Circle Created with python_avatars moninchow says:

    Great video

  28. Avataaar/Circle Created with python_avatars B J Lee says:

    Very interesting approach to solving the riddle! I have a 2004 Silverado that had the same issue – defrost only. Bought it used, did not know the history of the vehicle. Paid the diagnostics fee at the dealership, yup, that's right paid the diagnostic fee at the dealership to verify it was the mode door actuator. The tech was very knowledgeable and helpful. As you said re the mode door there is no wire to be able to monitor it without probing it as you did. He told me the mode door actuator failed, provided me with the schematic printouts for the system same as you showed following the colored wires. I bought a mode door from the dealer and left lighter in the wallet. I installed the actuator myself, bugger to get to and install getting the gear and dowel slot lined up. I tested the old actuator with an old 9V battery, it would rotate both ways, as the tech had said it was the feedback that was likely the issue. Fast forward about 3 months and the actuator failed again! Back to the dealership and spoke with the service department about the issue. They advised that as they diagnosed the issue, even though I installed it, it would be covered under the parts warranty. Fast forward since March 2020 ( yup, March 2020 ) and the actuator has not acted up since. My truck just turned 280,000 kms, so like 175,000 miles. Since march 2020 I have been working from home so the truck doesn't get used like it used to driving to work every day.
    I admire your approach to verify before throwing parts at it, my hats of to you. Should the actuator act up again I have more insight into how to prevent replacement, thank you. Mine hasn't blown out the door sealer foam dust, it doesn't get that hot up here in Kanuck-ville, and the winters begin in Oct and leave in April. Thank you for an informative video, I've watched many on the "GM Mode Door" issue. None of them were much help, that changed today. Cheers Mate!

  29. Avataaar/Circle Created with python_avatars Desarae VanStory says:

    My 98 Silverado is doing pretty much the same thing except the little levers that slide in the guide groves broke. And my AC just stopped working all together so now the heater works on high only all other functions have stop completely. I generally don't mind working on my truck… But I'm not about to take that whole dash out…. Any thoughts on a quick fix?

  30. Avataaar/Circle Created with python_avatars TreasureSweeper says:

    Mine just started not working and this was the perfect vid. Now I know what I need to do to start the repair.. appreciate your time and effort makin the vid…😉

  31. Avataaar/Circle Created with python_avatars Chris Bentley says:

    I just love these puzzling ones and how you figure it out. Great video.

  32. Avataaar/Circle Created with python_avatars Craig Chadwick says:

    Had the same problem on a 2000 silverado GA truck 360k miles, I was just gonna live with it. Thank you so much

  33. Avataaar/Circle Created with python_avatars Ozzy Krahn says:

    what happen to cables

  34. Avataaar/Circle Created with python_avatars Brian O says:

    Wow! You’re Einsteins lost brother😆

  35. Avataaar/Circle Created with python_avatars Daddyoh says:

    Excellent troubleshooting, did you get approval from the shop owner to add the screw to the door motor. lol.

  36. Avataaar/Circle Created with python_avatars John Quinlan says:

    THANK YOU!!!
    Been messing with this for a while, this makes sense

  37. Avataaar/Circle Created with python_avatars D Conservative says:

    Odds are slim I would have ever thought about the insulation on the blend door causing overshoot and loss of control. Great attention to detail. Wish I knew where you get your wing diagrams and tech data. Thanks.