1660240508587 Paulstudebaker

Things we know are changing so fast, we no longer know for sure

May 28, 2019
Negative knowledge is a dangerous thing, but so is thinking you know the answer when your wisdom is wrong or outdated

Back in the magnet factory, we had a department superintendent who, it seemed, could never give a straight answer. Instead, he would tell you a long narrative with many clauses, digressions and interesting words, but no substance. We called it “negative knowledge”—after listening to Bill, you knew less than before you asked the question.

Negative knowledge is a dangerous thing, but so is thinking you know the answer when your wisdom is wrong or outdated. I was recently reminded of this when doing the simple task of changing a set of rack boots on my car. Rack boots are rubber accordions that seal the joints between the steering rack and the inner tie rods, with a big inner diameter clamped at the rack housing, and a small outer diameter clamped around the tie rod. I found mine broken while replacing some other suspension parts, so I ordered a set and, while I was waiting, decided to remove the old boots.

It’s an obvious and simple job, but I always like to review the shop manual, which was explicit—the first step is to remove the outer tie rod ends. That’s a little fiddly because you want to put the ends back on in the same position to preserve the wheel alignment, so you mark them and count the turns it takes to unthread them. The right side went smoothly and soon that end was off. The left side was seized, so I progressively deployed my arsenal of penetrating oils, larger wrenches and eventually, the Mapp gas torch, all with no success. After a couple of hours of that, I gave up, decided to replace the tie rods, put a set on order and planned an alignment after all.

But when I continued on to remove the boots, I discovered that, unlike any others I’d done, instead of a small outer diameter, these have a large outer diameter clamped around a rubber donut that is part of inner tie rod—they fit over the outer tie rod ends and can be replaced without removing the outer tie rods. D'oh. If I'd looked it up on the forums, I would have saved a couple hundred dollars as well as the time (and danger) of the escalated wrench and torch work.

Not long after that job, my son in Tucson came home from work on a Friday evening to a broken central air conditioner. Daytime temperatures were already over 100 °F, so he called to ask if I had any advice on fixing it. The air handler was running but not blowing cold, so I directed him outside to the condenser unit, where he found the compressor grumbling but the fan standing still. I told him it could be a bad fan motor, wiring or contactor—all, I thought, beyond his skillset and not likely to be fixed over a weekend—so I suggested he might try laying a box fan on the unit and seeing if that would let it work. He bought a cheap box fan, but for some reason, it stopped running after a couple of minutes. I said he should probably call for service in the morning.

Later that night, he texted me that he had read on the web about motor starting circuits and capacitors. It said to try giving the fan a spin with a coat hanger, so he did, and it ran. But after a while of blowing cold, the fan turned off and didn’t restart. I texted back about calling for service in the morning.

In the morning, he texted me that he used the Fluke meter I gave him to test the capacitor. One side read normally, but the other side read zero, and where can he get a capacitor? I congratulated him on not electrocuting himself (and myself for giving him the meter), and told him they come from appliance parts stores, or from HVAC or motor shops, which are closed on weekends. A few minutes later, he texted back that Amazon would deliver the correct capacitor to him on Sunday. By Sunday afternoon he had fixed his A/C for a total of $18.

I think my knowledge is still more positive than negative, but I’m no longer assuming anything. The crowd has the latest information, the web makes it easy to find, and the logistics (an A/C motor capacitor on Sunday!) are flat amazing. Live, and learn.

About the author: Paul Studebaker
Paul Studebaker, Editor Emeritus, Control. Reitred from full-time employment in January 2020, Studebaker earned a master's degree in metallurgical engineering and gathered 12 years experience in manufacturing before becoming an award-winning writer and editor for publications including Control and Plant Services

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