Stuck for two days on a door zone fault that was just a bad limit switch

Got a call for a hotel downtown where the elevator kept stopping about six inches high. The controller kept throwing a door zone fault. I checked the sills, the hanger rollers, the whole door operator assembly. Spent maybe 16 hours over two days on it, tracing wires and checking voltages. Finally, on a hunch, I swapped the up limit switch on the car top. The old one was just worn out and sending a weak signal. Has anyone else had a simple part failure mimic a bigger system problem like that?

3 comments

3 Comments

fox.jesse3mo ago

Man, you ever just carry a spare limit switch in your kit now? I got burned by a bad down limit doing the same thing last year. It would pass a basic continuity check but fail under load. Took me forever to figure out it was a voltage drop issue. Those weak signals drive the controller nuts.

blair_green863mo ago

Carrying a spare seems like overkill to me. A proper load test with a meter would catch that voltage drop issue before it causes trouble. I'd rather spend time on solid testing than packing extra parts.

nathan_webb1mo ago

Hooked a multimeter up to the coil circuit while it was under a full load, that's how I finally caught mine. The voltage would drop from 24 down to 10 or 11 and the relay would chatter before locking out. What really threw me was the switch looked fine physically, no corrosion, clean contacts, even passed a resistance test cold. But after twenty cycles the internal spring would get a little slack and the voltage drop happened on the last quarter inch of travel. Ended up swapping in a sealed reed switch with a higher contact rating and its been solid for two years now.