Garth S

Bill,
As Greg says, there is a thermal switch that fubars frequently - but most often, it defaults to speed 4 intermittantly .... no resistance.
I pulled the feed wire off the thermistor (without removal of the resistor block) on one, and all speeds are there ... for the last 5 years anyway

Bill Ball

Eh, I see, the contact between 2 and 8 interacts with the speed circuits.

Garth, so, you think pulling the connector to pin 8 might "fix" this?

Bill Ball

I guess I could have searched this a little more. Seems like everyboody has had this problem, and a new resistor pack fixed them.

https://rennlist.com/forums/showthre...=resistor+pack
https://rennlist.com/forums/showthre...=resistor+pack
https://rennlist.com/forums/showthre...=resistor+pack
https://rennlist.com/forums/showthre...=resistor+pack
https://rennlist.com/forums/showthre...=resistor+pack
https://rennlist.com/forums/showthre...=resistor+pack
https://rennlist.com/forums/showthre...=resistor+pack

I need to check the fan for excessive load.

RyanPerrella

I think this resistor pack is an $80 item, or close to it. You may just want to replace as you could spend some time cleaning and it still wont function properly.

I like that your trying though, your experience helps us all out.

carbonfiber

I had the same problem on my 82 and when I removed it I simply gave the conatcts that were touching a little air gap so that they wouldn't touch. The contacts act like a turn signal relay in the fact that when the Bi-Metalic strip heats up enough it deflects and makes contact with the other contact and there by bypassing any of the resistors to prevent them from burning out. I have had a year of daily driving on my repair and never had the high speed default since. I had read of this fix on another 928 site but don't remember where but was surprised that it was as easy of a fix as this because I was getting ready to order a new resistor pack also. Hope yours is just as easy.
Jim
1982 Silver 928
2000 Arena Red 996
1953 Adria Blue 356 (on to another caretaker)

Bill Ball

Just for the H of it, here's the wiring diagram. Note the 89+ is different from -88. This is 89. I tried to trace the flow. Some of it make some sense, some of it doesn't. I'm still rather challenged when it comes to wiring diagrams. Pin 2 and 6 on the resistor pack don't appear to connect to anything. The blower is fed from pin 8 or the other black wire which goes from the defroster relay. Everything else is Greek.

Bill Ball

Hmm...so, if I spread that contact, it should work? Weird. Doesn't make sense, as, at least with 89+, that's the only way pin 8 gets power unless the switch is in position 4.

macreel

Bill, if that picture is yours, you have a 'newer' resistor pack.
The older ones have no cage over the coils. Look at the coils
and be sure none are touching structure or base or cage.

Sometimes with temp and age the coils sag and short/burn out.
Mine did; I brazed in a piece of resistance wire from an old
oven element and it worked fine. Heinrich has it now using
it to diagnose his problem.

I put in a new pack(like yours) after S'fest '05. It works fine.
The 'repaired' pack is just a diagnostic tool now.

G'luck.

p.s. that bimetallic strip with the contact goes closed, with increasing
temp, so that full volts go to the blower and puts max air flow
over the pack coils, hopefully cooling them sufficiently.

Bill Ball

Macreel: the coils test fine and I get appropriate readings at various plug pins to which they are attached. It's the function of the thermistor that I don't get. It appears to need to be closed for current flow out pin 8 to the blower, at least for 89+. I'm just fooling around here, as I have a new pack coming from Roger.

Bill Ball

Here's the -88MY wiring. It makes more sense to me. Pin 6 drives the blower and the thermistor acts as a bypass when closed. At least that's my crude reading. They swapped a lot of things around on the 89+ model.

macreel

Bill: New is good.

BTW, is your "thermistor" = bimetalic strip ?? The circuit
symbol (on my '89 schematic) implies a thermal-mechanical doodad.

p.s. I've noticed that (sometimes) the reality and the schematic
don't agree, pin numbers wrong and 'wires' go to unreal places.
Which is NOT helpful.

G'luck & top of the Season to you & yours.

Bill Ball

It looks like a common points contact. However, there is a very tiny piece of metal that is concave that is wedged between the arm and base. You can't see it at all until it falls out when you pull the contact wide apart. One side is marked with the letters CE. So, maybe that is the bimetallic piece. It fell out and I can't quite determine how it goes back in (which side up). I'm doing my best to avoid some last minute Xmas shopping.

IcemanG17

Bill
Did you pull the hood to get the blower out??? I cant remember if your recric flap was leaking...but since you already have the hard part done might as well change the recric flap too.....its only a $20 part.....I have one I don't plan on using for a couple weeks (at best)....

Bill Ball

Brian:

No, all I did was push the boot down between the blower and the inlet. Didn't touch the blower. Fortunately, my recirc flap is fine. The only AC actuator that is leaking is the floor vent. Thanks for the offer.

Merry Xmas!

danglerb

I would be tempted to replace that mess with a modern PWM variable speed controller.