Case of the Vintage Furnace Blower

Rob Spiegel

December 21, 2011

2 Min Read
Case of the Vintage Furnace Blower

When my father passed away, he left us with a house to sell. Since winter was setting in, the fact that the furnace blower motor would often fail to start when the thermostat called for heat was a big problem. Also, since my sister was living in the house at the time, it was important to have the furnace working properly.

The furnace was an old Lennox gas model (vintage 1955) with an air blower powered by an induction motor with an attached speed control. Because we were not interested in spending thousands of dollars on a new furnace for a house we wanted to sell quickly, we decided to call someone in to repair the blower.

The repairman arrived the next day but was baffled as to why the blower was not working. His recommendation was to get a new furnace. As he was tinkering around with a furnace that was much older than he was, I happened to remember something my father did when this furnace acted up, in the same way, many years ago when I was just a kid. He used to take off the side panel to expose the blower motor and turn the speed control switch to a new position. This procedure allowed the furnace to operate for a while (perhaps a few months) until the process had to be repeated.I suggested this to the repairman, so he went ahead and turned the speed control knob. This caused the blower to spring into action. The problem was, the next time the blower motor had to start from a standstill, it would not start at all. This meant that a more permanent repair was required. When I asked the repairman if a new switch was available, he said it would be easier to bring about world peace.

So there we were, stuck with a furnace that needed periodic tinkering to keep it going. That is when I decided to take matters into my own hands. Upon taking the speed control switch apart, I noticed that the movable contacts were burned beyond recognition. Since I was willing to accept the loss of having various motor speeds, I decided to solder each movable contact (or what was left of it) to its adjacent stationary contact. This procedure allowed the furnace to work reliably for the two winters that passed by until we finally sold the house.

I have learned at least one thing in life: It sometimes pays to look over someone's shoulder while he's at work.

This entry was submitted by John Mitchell and edited by Rob Spiegel.

John Rapka is a design engineer at Warren Controls Inc. in Bethlehem, Pa.

Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.

About the Author(s)

Rob Spiegel

Rob Spiegel serves as a senior editor for Design News. He started with Design News in 2002 as a freelancer and hired on full-time in 2011. He covers automation, manufacturing, 3D printing, robotics, AI, and more.

Prior to Design News, he worked as a senior editor for Electronic News and Ecommerce Business. He has contributed to a wide range of industrial technology publications, including Automation World, Supply Chain Management Review, and Logistics Management. He is the author of six books.

Before covering technology, Rob spent 10 years as publisher and owner of Chile Pepper Magazine, a national consumer food publication.

As well as writing for Design News, Rob also participates in IME shows, webinars, and ebooks.

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