Blower Motor Malfunction
Before you spend a whole gang of dollars, try this: Have your mechanic take out the resistor pack that controls the AC speeds. Its' just in front of the firewall in the center, above the engine inside a plastic shroud. Check the resisor values with a multimeter or ohmeter. Also have him look at the points at the end of the bi-metal strips in the pack. Time may have caused them to lose their temper to the point where they're too close together. There should be a gap of around a sixteenth or maybe three thirty seconds of an inch when they are open. If not, have him bend them out to that tolerance. It worked for me not too many months ago, and even if it doesn't cure your problem, you have eliminated that as a cause without spending more than a half hour's labor.
I was able to remove/replace heater blower resistor pack with some difficulty, but without disturbing the hood or the blower using the following procedure:
-Remove thin black plastic cover and moulding at base of windshield covering the blower housing area.
-Disconnect (remove battery ground first !) resistor pack electrical connector.
-Remove screws holding pack, hold pack gently with long pliers and let gently drop onto blower duct floor.
-Carefully fold back part of the rubber sleeve connector that is between the blower housing and the duct housing.
-Use a long stiff piece of wire, put small hook in one end.
-Insert wire into duct through rubber sleeve, snag pack, carefully extract.
-Replace same way, reconnect pack and battery.
*Tom Robertson; '84 928S, 5spd., U.S.
I had an intermittent problem with my blower. Sometimes it would blow
at level 1 or 4 only, sometimes all levels. Then I realized the A/C
was not kicking in at all.
Turned out the in-dash control unit was bad - the relay that is an
integral part of it had blown. The part was about $400. I don't know
if the 86 unit is like the 89, but if the sensor/fan is not the
problem, it may be the control unit.
[see other 928 Tips for A/C relay replacement -Editor]
89 S4 5-spd Dk Blue/Gray
Fixed the Magic Blower Syndrome. Easy job !!!
This is what I did:
I pulled off the rubber weatherstrip/seal at the top of the firewall (firewall to hood seal). Now you can pop up the front of the big plastic drip pan and pull it out (the back of the drip pan fits under the cowl on tabs - no screws).
Under this plastic drip pan is the blower motor (on the passenger side), the black plastic evaporator housing (in the center), and the windshield wiper motor (driver's side).
Now, at about the middle of the car, just to the passenger side of the AC lines, you'll see a black, rectangular electrical connector, maybe 3/4" x 1 1/2" at the end of a wiring harness, plugged into the evaporator housing. Unplug this connector. It's a 7-pin connector I believe, and when you unplug it, you're looking at the back of the resistor block/pack. It's held inside the black plastic evaporator housing by 2 screws on opposite corners. The only problem is, the darn thing on the other side of the rectangular hole is too big to pull out through the hole! If you don't believe me, try it.
But.... if you are a bit thin (skinny?) you can open the boot that connects the blower with the evaporator housing, and reach in the housing with your hand. Yes: it can be done(!) ...but big hands and arms are no help with this job. Find someone to help you if required. Keep the top screw loosely in. Grab the resistor assembly inside the evaporator housing. Then have someone unscrew the last screw while you hold the resistor pack in your hand. When the last screw comes out, gently move the resistor pack out through the boot opening.
Next step: the resistor pack itself.
There are four spiral like resistors mounted on the assembly. They are 2,5 / 1 / 0,4 / 0,25 ohms. The resistors are switched by the dashboard fan control switch. Underneath the resistors is a bi-metal strip mounted that bypasses the resistor pack and connects full 12v to the blower motor. It activates when a certain temp is reached and triggers cooling down the resistor pack by the produced airflow. Also by bypassing the resistors the resistor heat dissipation stops.
I tweeked the Bi-Metal strip to open approx 2 mm. Also I moved the spiral a bit away from the Bi-Metal strip (it almost touched the bi-metal!!!) Then I tested it on a power supply heating up the 2,5 coil. Works fine now.
Finally: re-assemble everything again.
You've got what's referred to as Magic Blower Syndrome. When the resistor controlling the fan speed gets too hot, the blower kicks up to high to cool it so that it doesn't burn out. I'm a former Magic Blower Syndrome sufferer myself. After spending probably way too much time working through various issues of this problem, I think I've got things pretty well sorted out. In my case I did not have to remove the blower to change the resistor pack. It would take me maybe five minutes to get mine out now that I know how to do it. Below is the information I sent to someone once before that also had the problem:
Apparently this problem is pretty common. The fan speed is controlled by a resistor pack that is located in the engine compartment of the car. It's under the plastic cover by the firewall. When the resistor controlling the fan speed gets too hot, there is a thermal switch that kicks the fan on high speed to cool off the resistor with more air flow. Several things can possibly be causing the switch to kick in. The switch may be more sensitive due to age or something. The blower motor may be worn, or have debris or something causing it to drag. This causes it to draw more current and the resistor to get hotter. There is a rubber sleeve that connects the blower housing to the plastic housing that the air flows through. If this rubber sleeve isn't on right, it will allow air to escape instead of going through the housing and over the resistor pack. Less air over the resistor pack means less cooling and it getting hotter, potentially triggering the thermal switch. There is also a small plastic cover on the top of the blower motor housing. Mine wasn't on tightly. This also may also allow air to escape and decrease the amount of air going over the resistor pack.
The first thing that I did was to replace the resistor pack with a new one. The new one made things even worse. The fan was going to high much more often, even when it wasn't that hot outside. I really didn't notice if the rubber sleeve I mentioned above was on properly all the way around when this was happening though, since it was kind of hard to get at the bottom part of it. That loose small plastic cover on top of the blower motor housing hadn't been discovered at that point yet either. I took the new resistor pack back and put the old one back in. Before putting it back in, I bent open the gap on the points for the thermal switch by about 1mm. I also noticed that the resistor coil that controls the slowest fan speed was touching the thermal switch strip. I bent the coil up just slightly so that it wouldn't touch anymore. When the resistor block was in I made sure that the fan turned freely by hand (it did), and that the rubber sleeve and plastic cover were properly installed. Since then fan speeding up hasn't happened even once since. The newer model cars have a redesigned resistor pack. Looks like this started with the '90 cars. The resistor that controls the lowest fan speed on it has .5 ohms less resistance than the one on earlier cars. This should mean it will heat up a little less, and also that the slowest fan speed is a little faster than on the earlier cars. The faster speed means more cooling of the resistor. The thermal switch part has been changed too. Instead of the long metal strip, it's now a smaller blue plastic looking piece. If the resistor does get to hot, it will stop the fan until things cool off, instead of switching it to high speed. Not really noticeable, and much less annoying than the unexpected blast of air from the fan going to high.
It looks like the newer style of resistor pack should be able to be used in earlier cars, but the connector that goes to the resistor pack must be modified. The cover of the connector snaps off revealing the wires and round hollow terminals. On my '88 car, the terminal that is in the #8 position would have to be removed from it's spot and taped up. There are two wires going to this terminal. They both remain connected to the terminal, but the terminal isn't used. Next the terminal that is in the #6 position is moved to the #8 position, and the connector's cover snapped back on. According to the wiring diagrams in the shop manuals, this makes the wiring the same as that on the '90 and up cars that use the newer style resistor pack.
I was able to remove the resistor pack without too much trouble. I slipped the rubber sleeve off of the junction between the blower housing and the evaporator housing, and was able to get my hand in through the opening to reach to the back of the resistor pack and remove it. Loosening the three screws that hold on the blower housing may give you a little more room if you need it without actually taking the blower completely out. An assistant with smaller hands might come in handy too. Good luck.
'88 928S4 Black/Black "PORSCHE" cloth
928 Owners Club Charter Member
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