Defrost fan rehab and rebuild thread (fresh air fan), or How the heck do if fix this thing? |
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Defrost fan rehab and rebuild thread (fresh air fan), or How the heck do if fix this thing? |
DRPHIL914 |
Jan 21 2021, 08:55 AM
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#1
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Dr. Phil Group: Members Posts: 5,766 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
I have been dealing with this for 12 years, a non-running defrost fan. i even pulled this out 2 years ago and rebuilt it with new flapper seals and main body seal then made sure fan turned but didnt bench test the motor or resisitors, so as a result it still does not work properly. i will be documenting this because 914rubber and Mark will soon be putting together a kit for this that includes all the hardware seals and even a motor i believe, BUT i still have problems and questions!!! so i am starting this thread to get information on diagnosing the common causes of it not working and how to fix it, and then document the rebuild and replacement of the motor, fan, resistor and maybe the control unit in dash. Others have documented the reinstallation of the fan and the cables so i will not duplicate that. and we may want to link other threads hear that have done that as well.
Mark is sending me a kit soon, so while i wait for it, i will have to get some more information about the wiring and resistors function and how to test them . I had this out last week and tested 3 different control units due to thinking that my issue was a control issue, because it runs on one speed, #2, and anything else does not work and it will then throw the fuse. most assume this would be caused by bad slider unit but i tested 3 of them and 2 are like new with no wear on the sliders , still same result. so i am suspecting the resistors /plug aparatus . If anyone has done this and cares to share how to examine and test that for proper function, lets start there. Resistor function, which lead is which and examination of the control units I will take pictures of mine tonight and post those soon. once this figured out and fixed i will do a full step bystep on reassembly too. Looking for lots of help and input on this, thanks!!! Dr. Phil |
Superhawk996 |
Jan 22 2021, 09:16 AM
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#2
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914 Guru Group: Members Posts: 5,812 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
Not trying to be a kill joy on the DigiKey resistors but I suspect that in the desire to find a nice "modern" looking resistor you've over looking the physics and the cooling requirements.
These packaged high watt resistors require a heat sink to last. Once that aluminum case gets hot and has no heat sink to pull the heat away, it will get too hot and burn open in short order. That's why I referenced the idea of wires exiting the HVAC case and having to mount it on the sheetmetal body as a heat sink. Likewise, that style of heavy resistor if left unsupported within the blower case is going to fatigue the OEM resistor standoffs that were not designed to support that kind of resistor weight when dynamic road loads are imposed on it. A thick gauge wire wound resistor in open air is going to be able to handle more current and heat rejection than a nice neat ceramic or aluminum heat sink package that looks aerospace cool. I look at it as the industry having converged upon the best, most cost effective solution and it's not one of those DigiKey style resistors. Poke around on internet and you'll quickly find the converged solutions are resident in the blower case, they are air cooled. Typically open wire coil, large ceramic, or Solid State with big honking cooling fins in the air stream. You'll notice in a couple that the bi-metallic thermal cut out switch has been replaced by a more modern component though! https://www.finditparts.com/products/594700...ASABEgJSDfD_BwE https://shop.advanceautoparts.com/p/bwd-hva...mp;gclsrc=aw.ds https://www.walmart.com/ip/Blower-Motor-Res...BCABEgI7CfD_BwE |
bbrock |
Jan 22 2021, 09:03 PM
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#3
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914 Guru Group: Members Posts: 5,269 Joined: 17-February 17 From: Montana Member No.: 20,845 Region Association: Rocky Mountains |
Not trying to be a kill joy on the DigiKey resistors but I suspect that in the desire to find a nice "modern" looking resistor you've over looking the physics and the cooling requirements. Wasn't trying to find a modern looking resistor. I was just trying to find any suitable replacement. I was actually searching for open coil resistors like what are in the blower and shocked not to be able to find them among the 500,000+ resistors in their catalog (or anywhere). I'm not saying they are not there, only that I couldn't find them. I am a bit offended though. (IMG:style_emoticons/default/happy11.gif) Even I'm not dumb enough to try to hang one of those chassis mount resistors from the OEM standoffs. I envisioned mounting to an aluminum plate, glued to the base of the resistor pack, and connected with flexible leads. Irrelevant if they are not suitable. I'm still puzzled why open wire coil resistors are not easier to find. Even resistor wire is kind of hard to find. All the stuff I've seen is annealed and too soft to make those spring like coils. |
bdstone914 |
Jan 23 2021, 12:18 AM
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#4
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bdstone914 Group: Members Posts: 4,520 Joined: 8-November 03 From: Riverside CA Member No.: 1,319 |
Not trying to be a kill joy on the DigiKey resistors but I suspect that in the desire to find a nice "modern" looking resistor you've over looking the physics and the cooling requirements. Wasn't trying to find a modern looking resistor. I was just trying to find any suitable replacement. I was actually searching for open coil resistors like what are in the blower and shocked not to be able to find them among the 500,000+ resistors in their catalog (or anywhere). I'm not saying they are not there, only that I couldn't find them. I am a bit offended though. Even I'm not dumb enough to try to hang one of those chassis mount resistors from the OEM standoffs. I envisioned mounting to an aluminum plate, glued to the base of the resistor pack, and connected with flexible leads. Irrelevant if they are not suitable. I'm still puzzled why open wire coil resistors are not easier to find. Even resistor wire is kind of hard to find. All the stuff I've seen is annealed and too soft to make those spring like coils. @bbrock I can supply you a good used resistor assembly. |
bbrock |
Jan 23 2021, 02:04 AM
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#5
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914 Guru Group: Members Posts: 5,269 Joined: 17-February 17 From: Montana Member No.: 20,845 Region Association: Rocky Mountains |
Not trying to be a kill joy on the DigiKey resistors but I suspect that in the desire to find a nice "modern" looking resistor you've over looking the physics and the cooling requirements. Wasn't trying to find a modern looking resistor. I was just trying to find any suitable replacement. I was actually searching for open coil resistors like what are in the blower and shocked not to be able to find them among the 500,000+ resistors in their catalog (or anywhere). I'm not saying they are not there, only that I couldn't find them. I am a bit offended though. Even I'm not dumb enough to try to hang one of those chassis mount resistors from the OEM standoffs. I envisioned mounting to an aluminum plate, glued to the base of the resistor pack, and connected with flexible leads. Irrelevant if they are not suitable. I'm still puzzled why open wire coil resistors are not easier to find. Even resistor wire is kind of hard to find. All the stuff I've seen is annealed and too soft to make those spring like coils. @bbrock I can supply you a good used resistor assembly. Thanks Bruce, Mine's actually in excellent condition and working well. I was just curious what replacement options for resistors were. It shouldn't be as hard as it seems to be. I get a perverse pleasure out of such challenges. |
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