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 21 2021, 12:29 PM
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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 |
I'm here to help. Not trying to be a jerk. Apologize if it's coming off that way, I'm an engineer so it comes naturally. (IMG:style_emoticons/default/laugh.gif)
https://www.youtube.com/watch?v=9LaV8lSdOHQ I have a copy of Prospero's garage laminated schematic. Nice for some things like color codes but sucks for others. Not sure if this is what you have. For the ventillation fan work, it is closer to sucks. The fresh air fan has no component detail on what in there, only a block diagram. Haynes manual is better IHMO. @bbrock recently tore into his resistor pack. I can't seem to find the thread at the moment. There are two wire coil resistors. They control Low and medium. High is wired w/o a resistor to motor per Haynes (white wire) . There is also a bi-metallic thermal cut out switch per the Haynes schematic. The resistors and thermal cutout switches can be verified with DMM. Unfortunately the Haynes manual isn't clear on how the bimetallic switch is physcially built. Brent's photo's I think had detail. The Haynes manual does show that if the switch is closed, it bypasses the resitor, drives the fan at full speed, and then cools off the wire resistor coil, at which point the bimetallic switch should open again and slow the fan to proper speed. With respect to the control levers, have you verified the connections and continuity with DMM? "so i could have 3 controllers that all have exactly the same issue OR more likely the issue is at the fan and resistors" As you state, you could have 3 bad units (not likely) but a quick continuity and/or resistance test with a DMM will verify them and remove any doubt. That is sort of what I was implying by making assumptions. Don't assume that and/or jump to conclusion is at the fan and resistors. Not trying to beat you up on this. It's a very common thing to do that can lead you astray and lot's of people make these sort of inferences when trying to do electical work. Comment above from @framos914 is spot on as we was basically using a half split method either knowingly or by intuition. The reason I mention DC motor theory is because if you have a motor that isn't free to spin (bad bearings/bushing) it will draw more current than it should and could blow the fuse and/or not even rotate on the lower speed. Likewise, if you have shorted windings in the motor, it could blow fuses. We can verify each of these possibilities in a methodical way. But, let's not get ahead of it yet. |
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