GMC Sierra: Stuck On Defrost

50 thoughts on “GMC Sierra: Stuck On Defrost”

1. Guess I failed to mention in the video that customer had all ready purchased a new OEM actuator. Just to be sure I wasn't crazy I tried it but knew it wasn't gonna work from our test results. He told me to just leave it in because he already bought it. 🤷‍♂️

2. Warpath coffee is the best coffee .

3. KATHUNK it all falls into place when I am able to use your videos as a reference place. Thanks for not only the fix but the theory and operation

4. Thanks for posting this video. I had a mode door actuator that was stuck on panel. I replaced the actuator with a new one and, after recalibration, it got stuck on defrost. I noticed little pieces of old foam blowing out the defrost vents and landing on top of the dash, and, because of this video, was able to assume the damper was over rotating due to the foam degrading and getting stuck. I removed the new actuator, installed a little screw to limit how far the actuator could rotate, reinstalled, and it worked! Thanks again!

5. Mine over ranges but the other way. I’m not sure what to do

6. The doors are metal with a rubber ring around the outside that contacts the box to seal the rubber deterates then you are out of range the foam does not stop the door I bought new AC Delco doors

7. i wish you just installed a new part and explained and showed how to line it up…but you obviously are a great mechanic.

8. $800 labor job😢

9. The Amazon mode door I just removed has a screw placed to limit door travel though the foam appeares to be intact on this one.

10. On a 2001 Silverado there is no relearn. Take out 4 bolts and take the driver's seat out. Makes it a whole lot easier. Mine had a cracked main gear in the actuator. If it's stuck on defrost the problem is probly a cracked main gear in the actuator, a gear missing some teeth, OR the defrost flap gear NUB is going past the stopping point of the BIG gear with 3 grooves in it. The defrost flap is the upper most gear with a visible NUB popinting outwards. The gear for the defrost is probly slipping past the stop point ( end of groove where you can't see through it) which causes the actuator motor to go past it's limit and will stop working. The gears in the actuator can be replaced, order gears online. DO NOT get the potentiometer gear out of clock. You can get it 180 degrees out..(I Believe). In the upper most groove, for the defrost flap, put a screw in the groove (to stop the flapper NUB from going to the end of the groove) or fill the groove with JB Weld about a 1/4 inch from the closed end. Worked on mine for 2 days until I saw the BIG grooved gear go past it's limit and stick in defrost mode.
    
    I tried the cotter pin but the flapper gear NUB would slide over the cotter pin. So, I put a screw in from the outside in to stp the nub a 1/4 inch from the end. Working just fine now.

11. thank you.. i just had to fix mine while sitting in the driveway

12. Brilliant! 🙂

13. Brilliant! Thank you so much. Bug help.

14. Hello, what brand and part number is that U scope that you're using in this video? Thanks

15. Thank you so much, I have the same problem and now I know how to check.

16. oh shoot! could you start over feller? I fell asleep. stop hanging around that looser scanner dan! I go into a coma with that guy

17. bla bla bla. just point the parts cannon at it and blast it! eric. the tec-no bleep bloops is putting me to sleep feller!

18. Thank you for the video. I had a busted gear in my actuator, changed it, and ended up having the same issue getting stuck in defrost. Reset the new actuator, stuck a screw into it, and bobs your uncle. Truck is a 01 gmc 2500hd 8.1 allison ext cab long bed 130k. Was a 1 owner truck and came from Nevada. I'm up here in PA and gonna do what is necessary to make it outlast me. If the dash should ever need to come out, I'll address the foam issues then.

19. Thank you so much. I’m having the same problem the flap door on the passenger side I believe got eaten up by rats so I’d always hear this knock knock knock now I know how to fix it. I’m gonna try the same thing.

20. What was the "calibration" of the screw? (About what was the amount of travel taken out?) 1/8"?

21. Had a 2003 1500 LS pick up I had this same issue on, replaced the mode actuator with a new Dorman unit, so many videos on how to but none of them explained and SHOWED the white door gear position as it relates to the position of the gear-toothed section on the black actuator upon install. 27 minutes shows this, one or two teeth in (depending on how you view it) match with the first tooth on the black geared part. Set the turn knob in the middle, reset the fuse, worked. Now the issue I have is the gears stick as it engages vent (dash only) mode / full stop to the one side. Probably new parts need to be worn in, there's just too much pressure on the assembly. I've tried loosening the mounting screws just so they barely touch snug, no dice, considered adding in a spacer washer between the actuator and the mounting screws to bump the whole thing out but then there would be less gear contact and probably not resolve the binding. This is just another example of a poorly over-engineered device that cons people out of their money and time when a simple slide lever attached to a cable and spring to each flap door would work fine, as it was for so many years. But nooooooooo.

22. Thanks for the great video❤

23. Awesome problem solving

24. thanks for the video my truck is having the same issue and i replicated your fix and it works as should thank you

25. You’re a smart feller!! This problem has been driving me nuts for two years on my old truck! Fixed! Thank you for making videos!,

26. It’s not a hack if it’s usable and works merely a alternative

27. yup i was trying to figure this out for 12+ hours and just stumbled across this video, put a screw in and voila it works good as new.
    Thanks Eric!

28. Have an 01 silverado 2500hd 8.1L. Was shifting hard in 1st and 2nd gear. Changed the TPS and now only shifts hard in 1st gear. Tranny shop can't find anything wrong. No engine or tranny codes. Fluid is good, throttle body is clean, RPMs, and Speedo run fine. Does not matter if hot or cold. Sometimes feels like it's the rear end and other times the front. Any thoughts on what to look at?

29. Is a video any chance of how to get the actuator with the door in im having trouble

30. Which fuse should i take out to recalibrate actuator?

31. I spent the better part of 3 hours on a 1.5 diag today for this exact issue. I truly appreciate you filling in the gaps for me. I was on the right track I was just lacking the knowledge and experience. I can definitely get a better angle of attack on it tomorrow. Thank you.

32. How far up did you put the screw compared to the position of the pin

33. Dude, It's late so I'm not checking now, but my truck has stopped spitting out foam for a long while now, and it's also stuck in defrost. You may have just solved me a ton of time and some cash. Thanks.

34. I'm having this exact problem. 2002 Yukon XL. Psyched to find your video. I'm no good at checking the electrical stuff so I'm just gonna try your method. I'll check back in. Thanks for the thorough report!

35. I have a 97 GMC k1500 and it has the EXACT same issue. i am NOT a mechanic in ANY sense of the word, but i am also not afraid to watch Youtube and get my hands dirty. This video had SO MUCH awesome information in it. Not just the issue with the actuator, but also taking off that plastic panel to get access to all the dash panel stuff. I want to swap out the stereo that the kid who owned it before me put in. Thanks so much for going slow, explaining EVERYTHING, and showing it all!

36. This was a long time ago you produced this video, and I followed every step you made with the logic. Great diagnosing, very accurate.
    The method of using a pot (potentiometer) to vary the voltage driven by gearing attached to a given measured arc is interesting. You remind me of me when I go out on service calls and have to diagnose automation systems of pools or mechanics.
    Just work by myself now, but when I worked for other shop owners they had no patience with me, just replace parts and charge the customer.
    Our type of diagnostics is what brought back Apollo 13.

37. We replaced our actuator as 8t was blowing heat.
    Now stuck in defrost mode! 2000 GMC Sierra in AZ!

38. Very helpful video!! Yep, I have the same issue with my 99 Silverado. Little bits of foam have been blowing out of the dash air openings for years. Never paid much attention to it, until now. I’ve replaced 2 of these actuators in the 26 years I’ve owned the truck. The second one did the same thing on full defrost, it got stuck in that mode. I’ll probably do the screw rig into the new actuator……or never go full defrost. Just use the blend floor and defrost setting. Which should be fine unless someone turns the knob all the way to full defrost.

39. After spending about 8 hours down under there on my 2002 suburban I got her fixed with the one screw to limit the travel on the defrost door in the hidden section of that groove thanks a million my guy. You're kind of a big deal to a lot of us.

40. great info. brillant repair. did you actually replace the motor unit?

41. My 2002 Suburban did this when I replaced my battery it just came out the defrost vents only.

42. I currently have the same problem and bought the new part to find out that it didn’t work. I looked everywhere and all of a sudden your video popped up on my phone. You saved me a whole lot of heartache. I’ll be doing the same thing you did and I hope it works. Thank you so much for all that you do for us who don’t know what is wrong with our parts.

43. My truck goes to defrost and will come out of defrost. But the air does not come out of the floor vents. It’s a real pain in the butt. I’m going to pull the actuator off and see if I can manually make the doors turn to get more floor vent air. Hopefully it’s just junk holding the door up.

44. hey, I have similar issues. Defrost only works and only on the centre vent window. A lot of small seeds and bits of grey lint keep shooting through. I hope I don't have a mouse living in there because it stinks. This video has given me hope tho. might try a couple things. thanks

45. This could be far fetched but ill give it a try anyways, i have 2011 acadia and i changed 6 mode door actuators since 2015 this time when it went out i decided to try and troubleshoot as much as i can i reseted hvac by pulling fuse for 1 minute and when i put it back in it did its little recalibration and i watched actuator go from maxed one way to maxed other way and than it went back to other max side and never returned so i tried changing modes and nothing happend , so i took actuator appart and took gears out and that little motor thats in there was constantly spining causing gears to lock up whilst not moving in modes so i turned hvac off and motor was still spining i got new actuator and it was doing it on that one too nothing has been done everything been working fine till it didnt so i didnt bother checking wires or anything else cause why would i if nothing has been touched , so my question is what do you think could be the issue ? Ps i did plug my scanner and i went into test mode and i can see when im pressing buttons i can see values change so i assume the board is ok since its responding to buttons being pressed

46. Like that i,Robot movie. "Your logic is undeniable"

47. Same thing happened on my 2002 GMC and I did the same thing you did! Now the blend door clicks over and over again unless on fresh air so I guess I get to see how hard it is to change the blend door actuator. Wish me luck and thanks for your videos! I really appreciate you doing them. I’m in Louisiana and you sure don’t sound like your from New York! lol😊

48. OMG what an outstanding video South Main!! I have been fighting the same problem with my 2001 GMC for months! It goes to defrost and won't return. I am on my third OEM actuator and have pulled out a lot of gray hair trying to figure this out. I was at my wits end when I found your video. I did confirm that the original actuator was bad as it wouldn't move at all installed or removed and slaved in. I am going to install a screw in the defrost door track and see if the foam is the problem, although I don't have any extra foam floating around the truck like you did. Thanks a million and I will update my findings.

49. First off. Love the theory and diagnosis in this video.

    I have one question though. I believe I have the same issue. Once the actuator reaches past its stop point. How do you get it to move back into position to be able to get it to move again. Totally understand the screw “limit” fix gonna attempt it but I’m stuck at beyond defrost and I can’t get the actuator to move back do i have to manually apply power to it to get it to go back or can i pull a fuse to reset it. ? That’s where I’m currently stuck (no pun intended)

50. What meter/oscope is that you are using? Excellent video by the way!

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