Sunday, December 30, 2018

Hey, it's 40 years old....

So I get the call about 5 pm last night.

"The range won't shut off".

See, there is a neat relay/contactor setup that, when one (or all) of three light switches (left/middle/right)  is turned on, also turns on the air handler and enables the air compressor that turns the target holders. As it had always worked, no one had ever worried.

Until Saturday evening.....when it stopped working correctly. Turn off the lights and the big fan keeps running. Not what is spozed to happen.

As I am the closest member to the range, I get the call.

My first thought was to simply turn off the breaker and wait for another day.... But the breaker that controls the lights and fan also powers the sewage ejection pump and the heater for that small room where the pump is located. (And last time we had issues with the sewer pump, at least one idiot ignored the signs and used the terlet....with messy results)

So I opened the control box, hoping to see something obvious.
No joy.

And, of course, while it appears that (at one time) there was a diagram of some kind for guidance on the door, it fell off or was removed long ago, leaving only the glue behind to mock those who might need it.....

So I had to close contactors one at a time, and follow the wiring (which was really nicely done, it looked like the interior of an Otis Elevator cabinet) and figure out how the thing worked.

And, while it took an hour and a half, I traced the logic and figured which contactor was stuck.
Pried the welded contact apart, and (for now) everything works).
Kinda proud of that diagnosis. Haven't worked relay logic for over 25 years. But I can still do it. So it is (sorta) fixed....For now.

Simply worn out and pitted contacts. But all the others are worn as well.

Someone is gonna have to replace the contactors ....all 5 of 'em.
And, since there are only 3 of us that have the ability (much less knowledge) it's gonna fall on us. And since one is pretty much crippled, and the other is nearly 80 years old, it's gonna be me. 


Old NFO said...

Glad you were able to sort it out!

Phil said...

Nice job of diagnosing the problem. Depending on IF the contactors aren't obsolete and you don't have to come up with a newer model AND they aren't in too bad of a spot, it shouldn't take all that long to do.

Beans said...

When you do the rewiring, are you going to separate the terlet and the sewer pump off on their own circuit?

10-1 one of your plans is recreating the circuit diagram and making sure there's at least 2 copies in the office files and one on the circuit breaker box.

Nothing is as much fun as critical repairs at 1am on a bad night.

B said...

Beans: Not sure I can do a good enough job of sketching the entire circuit. Access is limited and I'm not that good at relay logic. Plus it's cold up there.

As for separating the circuit, it's a 220 40 amp branch off the main box to a 4 breaker box up above the range. Not sure if I am willing to run another circuit all the way to the other end of the range (All I'd need would be 120/20 amp, but still it's 75 feet or more of conduit and I;m not sure it's worth it. I MAY run a single breaker off of the 4 breaker box, but that, again, is a cold job right now. May have to wait for spring for that, if ever.

Out of the 12 o or so members there are about 10 that actually do any work, and only one of those is an electrician, and he's retired and pretty crippled up. So it is me. and I got other things to do. So we will see if and when. Maybe.

DTWND said...

I think what you describe is called “institutional knowledge”. In the FAA, rules and procedures would be written to prevent/cure a problem. After a few years someone would be selected for plans and programs. They would be tasked with updating the SOP. This person would
change a word or phrase to what he thought it should be. A few years later, someone else would take over the job. They would update the SOP, dropping and adding their own input. After only 5-7 years the original problem would reoccur and then someone would write into the SOP what hand been dropped over time. History repeating itself.


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