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]

OK finally last night i was able to sort thru the wiring issues, figure out the proper positions for the fan wires, verified all the connections, the DAPO had list the plug housing and had not put them back in correct positions, with that corrected the new fan tested out and all 3 speeds work perfectly. before reinstalling i tested the other controllers and verified working along with my other 2 fans, those do work but not as well as brand new, so those will get rebuilt with new fans and hardware and seals. i will have 2 lower fan units that will be available and i can vouch for the resistor packs in both testing and bench tested and fully functional. this will be for sale soon if anyone needs one.
i struggled with one upper box unit that had a crack and was slightly warped, so the seal would not fit, that one had to be trashed, luckily i have a couple, 2 good ones so back together with new seals and clips.
i used Ian’s video suggestions of using rubber bands to hold the sucker in place when reinstalling the box. the seals are tight but my biggest issue was the warping of the top edge of the box.
the other issue with this is you have to pull the tank that’s a pain.
a few pointers:
1. don’t forget to put the connection for the fuel level sender back on before the expansion tank is reattached.

2. put the air duct hoses on before the tank and expansion tank because the passenger side is almost impossible to do otherwise.

3. new cable slide so nice and smooth, put them in , it’s worth the time.
- and the air box cable must be attached before box is installed .
installing thie box would be a lot easier if that cable were longer, due to its length it’s so tight it’s hard to angle the box or pull it out far enough to get the box at the right angle to slide it into place.
4. use a clamp like Ian did in his video or a pry bar for leverage to push the box up into place far enough to ge the box mount screws into place.

So i hope i don’t have to do this in this car again, but i am glad after 12 years i finally have a full functional defrost fan, and wiper mechanisms, and soon to be a new 911 motorized windshield washer pump conversion too. , while all this was open i added the wiring and the washer tubing, which no longer goes into the cabin. i installed a Carmagic switch into the column with my new levers i got from 914sixer. so that can be installed this week too!

Done!!

@Mike914 Mark thanks for making all the great parts and seals for the air box,
914rubber is the only company that makes the fan to housing seal, the big round one, and the vent seals and flapper seals!
these are now in their site for sale.

@UROpartsguy Drew, thanks for the info on the fans and making an affordable part! the fan is perfectly balanced.