Defrost fan rehab and rebuild thread (fresh air fan), or How the heck do if fix this thing? Options

[DRPHIL914]

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

[DRPHIL914]

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.

I'm also going to throw another one out there. You didn't mention which fuse was blowing.

Is it pulling power from the proper fuse? Should be fuse #8 - 25A fuse.

page 72 post #1439



http://www.914world.com/bbs2/index.php?sho...290&st=1420

Here is the detail on the bi-metallic switch BELOW the resistor.

@bbrock problem was only two speeds. Fully acknowlege this is different than your problem but it does detail how the switches are physcially built if you wish to document this thoroughly.

(IMG:style_emoticons/default/aktion035.gif) hey its all good, sometimes things come across different in print, but really no offense taken, i can see that engineering mind go to work! my son and my nephew are both engineers, my electrons choose the path of least resistance (IMG:style_emoticons/default/av-943.gif) and went with the spinal biomechanical engineering( chiropractor) but really got into the functional biomechanics, always loved learning how everyting works , still learning and digging in on this stuff, but i digress---
- thanks for pointing out the continuity on the controller i will recheck that and compare the other units , i did that a few years ago so will recheck and document it.
- i have a free turning fan, that seems good on this unit , not my spare unit.
- mark and Matt are thinking similar in rebuilding the motor, new ones Bosch are $80 or so, not expensive, but not cheap either.
-i need to check but pretty sure its fuse #8 being blown
if its not that means someone has been messing around. I went thru the whole harness and fuse box when i installed the new box with blade fuses a few years ago. but again i need to not assume but re-verify.
then need to measure the resistance of these 3 circuits on each unit i have.
I wonder if the spring in essence is your resistor but is broken and we know the needed value, should be able to rebuild that i would think right?
first things first.

BTW @Superhawk996 - have read all your build thread since it started, you also have mad fab skills, wish i had the room for doing that kind of work, i had to outsource mine but that ended up being worth at the time, you know time vs money and i dont have a lot of either but still working so thats the way it went.

lots of great infor hear already, will get at measuring and checking on these items and get back here soon.

Phil

[Superhawk996]

I wonder if the spring in essence is your resistor but is broken and we know the needed value, should be able to rebuild that i would think right?

@DRPHIL914 Thank you for the kind words regarding the rebuild of my (IMG:style_emoticons/default/stromberg.gif)!

Just for clarity, it isn't a spring per se. It is basically a wire wound resistor without a housing just suspended in air. The resistive coil is exposed to air flow and is air cooled (like the engine). Pretty neat huh?

If the coils were touching one another, resistance would decrease. If it breaks or goes Poof and opens up, now you have infinite resistance. Either of these scenarios can be checked with a DMM.

In @BeatNavy 's case, if he had a stalled motor (or very slow spinning motor), the low speed resistive element probably got too hot both from too much current draw (from the stalled motor) and lack of cooling from no airflow and then the smoke got out. (IMG:style_emoticons/default/hissyfit.gif)

Not so simple to repair but not impossible in concept.

The resistive wire is a special alloy designed both for stable resistance per unit of length as well as good thermal properties (doesn't melt easily, stable resistance at various temperatures, etc.).

Here is the Wiki on what it could be.

https://en.wikipedia.org/wiki/Resistance_wire

Nichrome and Magnanin are the most common.

Much easier to find a donor and replace if it turns out to be a resistor.

If I had to McGyver something, I'd start looking at toasters for their resistive elements but that would take some real trial and error to understand if it could even be done. (IMG:style_emoticons/default/huh.gif) (IMG:style_emoticons/default/sheeplove.gif) More seriously speaking, I'd start looking to other more readily avilable domestic blower motors to see if I could find a similar wire resistive element and would cobble that. Alternatively, you could replace the resistor with say 12 gauge copper wire (zero ohms resistance) and you would esentially have two HIGH speeds. Or I guess, you could just bend the bi-metallic switch contact to be closed all the time. Same result - bypasses the resistor. That was what caused @bbrock 's problem.

With a little math we could roll (i.e. wind) our own. (IMG:style_emoticons/default/smoke.gif)

https://www.amazon.com/Nichrome-80-Gauge-Re...F9N7AHK43ZF4CP8

Many thanks to Brent for photographing and documenting that bugger!