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

[bbrock]

@Superhawk996 I can't believe you were able to dig that out of my thread. I had forgotten all about it. And yes, my problem was that my blower switch positions went low, high, high. So the blower worked in all positions, but medium speed was missing as it was going straight to high because of that little breaker gizmo.

As for repairing a blown resistor - how important do you suppose it is to use an open coil resistor. Would something like this work as a replacement?

(IMG:https://media.digikey.com/Photos/TE%20Connectivity/HS,-CGS-51.jpg)

https://www.digikey.com/en/products/detail/...A502R5J/2366322

It's funny. I have a roll of nichrome wire left over from a failed attempt to build a DIY plexiglass bender many years ago. I remember when I was trouble shooting my blower that I might finally get to use that wire to wind a new resistor. Alas, it was not to be...

[Superhawk996]

As for repairing a blown resistor - how important do you suppose it is to use an open coil resistor. Would something like this work as a replacement?

https://www.digikey.com/en/products/detail/...A502R5J/2366322

It would definately work in the sense of functionality.

I think the reason for the open coil resistors is available package space and better cooling.

Looking at the size of the linked resistor, 2"L x 1"W and about the same 1" tall, I don't think it would fit. Could it have leads soldered to the resistor and then soldered to the OEM resistor holder and then mount the thing somewhere? Probably. I would be concerned about potential for the resistor to get hot enough to melt or deform plastic at 50W if JB welded to the housing or something like that. Drill holes for wires to exit the fan housing and mount that style resistor to the body as heat sink? (IMG:style_emoticons/default/screwy.gif) Sure, depends on how bad you really need a low or medium speed. (IMG:style_emoticons/default/laugh.gif)

The key thing I don't know is how much current is the fan pulling at start up (peak in-rush) and what is is steady state operating current. Once we know that, we could properly size the resistors. 50W might be overkill? (IMG:style_emoticons/default/confused24.gif)

Maybe this weekend I'll go over to storage and retrieve my fresh air box. I know mine worked on at least one speed before I tore the car down. Might be a good time to check out my own motor and resistor pack too. I'm hoping to drive this (IMG:style_emoticons/default/stromberg.gif) by Fall so it wouldn't hurt to know my fan is up to snuff. (IMG:style_emoticons/default/rolleyes.gif)

Could measure my fan for operating current. But then I'm also supposed to be measureing my 017 CHT sensor vs NOS 012 over on the other thread. So much fun stuff to do so little time.

[bbrock]

As for repairing a blown resistor - how important do you suppose it is to use an open coil resistor. Would something like this work as a replacement?

https://www.digikey.com/en/products/detail/...A502R5J/2366322

It would definately work in the sense of functionality.

I think the reason for the open coil resistors is available package space and better cooling.

Looking at the size of the linked resistor, 2"L x 1"W and about the same 1" tall, I don't think it would fit. Could it have leads soldered to the resistor and then soldered to the OEM resistor holder and then mount the thing somewhere? Probably. I would be concerned about potential for the resistor to get hot enough to melt or deform plastic at 50W if JB welded to the housing or something like that. Drill holes for wires to exit the fan housing and mount that style resistor to the body as heat sink? (IMG:style_emoticons/default/screwy.gif) Sure, depends on how bad you really need a low or medium speed. (IMG:style_emoticons/default/laugh.gif)

The key thing I don't know is how much current is the fan pulling at start up (peak in-rush) and what is is steady state operating current. Once we know that, we could properly size the resistors. 50W might be overkill? (IMG:style_emoticons/default/confused24.gif)

Yeah, I was wondering more about the general package style than that particular resistor. The one I linked was just a random selection of twenty-seven 2.5 Ohm chassis mounted resistors that popped up on Digikey that had a nice picture since I didn't know particular power and dimension specs needed offhand. There are many options. For example, here's a 5w resistor only 0.6" long. https://www.digikey.com/en/products/detail/...5WM2D5/11650430

I was surprised not to find a selection of open coil style resistors on Digikey which makes me think either I don't know the correct search term to use, or perhaps that style has been superseded to a modern design for the application. With thousands of resistor options available for almost any given resistance rating, there are surely suitable off the shelf options out there.

I picked the chassis mount to look at because they are mounted in heat sinks for heat dissipation which seems inline with the original design. You could mount those to a small aluminum plate with heat transfer paste for even more efficient heat dissipation.