Looking for suggestions on how to diagnose the real issue, when I slide the fresh air blower fan speed control to max (far right) the fan stops & the fuse that has the tail lights & instrument lights blows. Given the location of the slider cannot get a great view, but I cannot see or feel anything interfering with the mechanism.
Any thoughts?
Michael
One thing that happens is the terminal gets hot and melts the plastic that is holding it. And things get out of place.
Sometimes this makes the metal at the end of the lever touch things it shouldn't.
If it were me. I would be removing the 3 lever unit... And inspecting top and bottom.
They are real hard to take out. I never look forward to it. And it becomes easy to bend the wires that are going into the Bowden tubes.
Another thing that happens is with the fan...it can get corroded in there and make it hard to spin.
With that.... You can take the whole fan apart... And clean and shine. Put 12v to it. See how well it spins.
But it sounds like the fan is spinning.
Current long term ownership: 63 Cab, 71 911, 74 914
THanks Scott, Happy New Year, re the bolt holding the 3 lever unit, is the nut supposed to be "captured", I can turn the bolt but it remains in place!!
Michael
In my shop when faced with a short circuit I approach this in a different way then most other techs do. Use the short to ground to your advantage. The fuse that blows has power on one side and a path to ground on the other making a complete circuit from the battery back to the battery. This is the reason the fuse blows. The fuse becomes the load (thing doing work) in the circuit. When there is no complete path from the battery positive to battery negative the fuse can't blow. Remember. All electrical flow starts at the battery and ends at the battery. Open the circuit anywhere and flow is disrupted. Create a path to ground before any loads and the fuse will blow to protect the wiring.
Remove the problem fuse and install a light bulb instead. The bulb will light when there is a short to ground. By using the bulb, you take the invisible problem and make it visible. I use an inductive current probe that clamps around wires and measures the amperage or current flowing through the circuit. Measure either side of the jumper wires going to the light bulb and make a note of this reading. Then move the probe along the wires in the circuit. You will have current all the way up to the short. Once on the other side of the short there will be no current. This means the problem is between the last reading of current and no reading of current. Alternatively you can disconnect things on the fused circuit looking for the short. Every time something is disconnected check the bulb. When the bulb goes out your on the right path.
I've used this method for years. It saves on fuses, wires and frustration. I personally use a 194 bulb as it requires little current to operate and I can keep it off the carpet more easily. The bulb will generate heat and melt carpets.
I hope this makes sense and helps. Electrical work really is not as hard as most people think. Just need to sit back and think about how electricity flows through the circuit.
Michael. I don't remember specifics of the nuts and bolts on that unit.
I just know it is hard to take out.
Use a lot of light.... And don't force anything. Go slow, even tho you don't want to.
It should be worth it to clean up that unit after 50 yrs.
Update: I looked underneath. I can't see everything. But it sure looked like my nut was welded onto the bracket.
You might need some small needle nose vise grips to hold what's spinning.
Last edited by Scott A; 01-01-2022 at 09:15 AM.
Current long term ownership: 63 Cab, 71 911, 74 914
Update: I looked underneath. I can't see everything. But it sure looked like my nut was welded onto the bracket.
You might need some small needle nose vise grips to hold what's spinning.[/QUOTE]
So I pulled the blower out of the trunk, & was a regular nut, so released the control unit, cleaned up 50 years of accumulated dust & grease , lightly sanded the contacts, & it seems the short is gone🤗🤗
Michael
The lever controls the ground connection to the blower motor, if it was positive there would be a real danger of short circuit to ground. A dirty switch might cause a current spike.
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