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System Design vs System Repair

I recently spent the better part of a Saturday afternoon helping a neighbor replace his car’s heater fan motor. Having spent many, many such afternoons (and mornings and nights) working on cars in my lifetime, and even though I previewed the project a few days earlier just to get an idea of the repair’s scope, I knew before hand that automotive projects beyond changing an air filter or checking the oil are seldom as simple as they seem. My neighbor’s fan motor repair project did not disappoint.

As expected, the fan motor was underneath the dashboard on the passenger side – just behind and to the right of the glove box. Heater fan motor assemblies are typically attached to a housing into which the squirrel cage blower is inserted. Once the blower is inserted into the housing, a flange attached to the motor mounts the assembly to the housing, thereby sealing the system to help reduce air leaks and improve overall air flow. With me so far? Good.

My neighbor’s car was just this type of assembly. Three screws, just three simple screws, held the fan motor assembly to the housing. I scheduled the project into a two hour block between a morning and afternoon commitment, hoping I could finish things up in about an hour, but leaving myself a full 60 minute cushion just in case I needed a little more time. I had the necessary tools, and my neighbor had already purchased the replacement motor assembly, so I thought I was set for a relatively easy automotive repair project – sort of like the proverbial “walk in the park” version of vehicle maintenance. With a cautious sense of optimism, I grabbed a handful of tools out of my toolbox and went to work.

Space and time won’t permit an every-turn-of-the-screwdriver project review, so I’ll cut right to the point of my story. I had to take apart most of the lower half of the passenger side dashboard in order to get to the motor assembly. Fair enough. Even a basic car has a lot of parts, and part placement is not always convenient. I even had to disconnect several electrical connectors – again, just an expected but simple part of the project. The “fun” part of the project started when I tried to remove those three mounting screws. Two of the screws came out without too much trouble. The third, however, was sort of nestled in the corner where the firewall meets the passenger side kick panel. Had to bend my body in ways it had not bent for years just to get at the screw. Then I couldn’t get a square bite on the screw head with my screwdriver, all because of an auxiliary fuse panel mounted just below the screw. The fuse panel stuck out just far enough to block my screwdriver’s direct access, and kept the screw from coming all the way out. Took me awhile to wiggle the screw out, then took yet another little while to figure out how to pull the motor assembly down out of its housing – even more stuff crammed into a tight space blocked what should have been a simple removal. But I was in for yet more fun…

After installing the old squirrel cage blower on the new motor assembly, I set to work trying to fit the new assembly back into the housing. Once the assembly was back in, I just needed to reinstall the three screws, reconnect the electrical harnesses, and put the dashboard back together. Simple in theory; not so in practice. That pesky third screw had different plans. Reassembly proved even more bothersome than taking the system apart. The obstructing fuse panel made getting the last screw in place a real pain. A simple solution would have been to detach the fuse panel – tried that, but couldn’t figure out how. I almost gave up several times, especially since the other two screws seemed to hold the assembly pretty well. But after more wiggling, jiggling, and twisting (both of my body and the fan assembly), the screw finally slid into place. By the time I attached the last piece of interior trim, I was 4 hours into my hoped for 1 hour project. Needless to say, I didn’t make my other afternoon commitment.

So why I am telling my latest story of automotive repair woes? Simply to finally say publicly what I have thought many times over the years when fixing cars in specific or other systems in general, especially when frustration levels rise directly with extended repair times and inversely with project success. I believe that system designers, whether automotive or otherwise, should also have to repair and maintain the systems they design, at least for a while. Sort of like an apprenticeship. In order to become a system designer, you would first have to be a system mechanic. I believe there would be far fewer “third screws obstructed by auxiliary fuse panel” issues. Repairs and maintenance would magically, mystically be more straight forward and a lot easier. I know there is probably a well documented procedure for replacing the heater fan assembly in my neighbor’s car, and the instructions no doubt clearly explain how to remove the auxiliary fuse panel. If I knew the procedure I may not have spent much more than my originally planned hour on the repair. But moving the fan assembly mount just a small quarter of an inch away from the fuse panel would have solved the problem without the added overhead of documenting the panel’s removal. Why document how to do something when a simple design change makes the process obvious? No rocket science involved. So when we get to the point in our design flows where we need to answer the “How are we going to build this?” question, we need to take a long look at how the parts will actually fit together – and how they will come apart – before moving a design from the computer screen or design drawing to something we can touch and feel…and repair.

And one more thing…whenever you schedule any do-it-yourself automotive or system repairs, at least double your initial time estimate. I guarantee the extra time will come in handy.

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About Mike Jensen

Mike JensenMost career paths rooted in high technology take many interesting (and often rewarding) twists and turns. Mine has certainly done just that. After graduating in electrical engineering from the University of Utah (go Utes!), I set off to explore the exciting, multi-faceted high tech industry. My career path since has wound its way from aircraft systems engineering for the United States Air Force, to over two decades in applications engineering and technical marketing for leading design automation software companies, working exclusively with mechatronic system modeling and analysis tools. Along the way, I’ve worked with customers in a broad range of industries and technologies including transportation, communications, automotive, aerospace, semiconductor, computers, and consumer electronics; all-in-all a very interesting, rewarding, and challenging ride. In my current gig, I work on technical marketing projects for Mentor Graphics' SystemVision product line. And in my spare time I dream up gadgets and gizmos, some even big enough to qualify as systems, that I hope someday to build -- providing I can find yet a little more of that increasingly elusive spare time. Visit Mike Jensen's Blog

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