TL;DR Summary: The Limitor part you are looking at (T160: Labeled Y59 B 120C or similar) is a thermal/current limiting switch. It has failed and is probably why your lights aren’t coming on.
A couple of weeks ago I flipped on the light to my kid’s room and I was startled by a PLINK and blue arc flash of death that signified that it was time to begin the ritual hunt knowing that there was, like, a 5% chance I would have any bulbs that would fit.
Oh, it’s not like the socket or bulb are anything special - I was just playing the odds with my Schroedinger’s Lightbulb Cabinet of Utter Inconvenience. Since I needed two 40W candelabra bulbs, it was likely I would find one 15W, one 40W standard socket bulb, and twenty-seven 100W outdoor flood lights. If I need a flood light, there would be a completely different distribution of stuff there. Maybe it would just be filled with scented candles and a whale oil lantern but it would almost certainly contain no flood lights. I’m sure you have a junk drawer or pantry shelf with similar qualities in your house.
So imagine my surprise when, lo and behold, there were two perfectly good 40W bulbs at the ready. Awesome. Let’s just screw them in and flip the ol’ switch and… nothing.
Hmmm…
The fan’s still working so maybe I didn’t screw in the bulbs tightly enough. Nope, that’s not it. Let’s try the pull-chain - I never use it, but, hey, you never know - while I was hunting for the bulbs maybe someone else in the house tried to be “helpful” and yanked the pull chain a random-but-odd-number of times (look, don’t even get me started…). No dice.
“The pull switch must have died when the bulb blew. Wonderful,” I thought. I shut off juice to the fan, removed the bulbs, took off the housing, removed the switch and took it to the garage so I could write down the info for a replacement. On a whim I screwed in the bulbs, got my multimeter, and measured resistance across the switch. Low resistance. I pulled the chain. High resistance. I pulled the chain. Low resistance again. Everything was fine.
Again, hmmm…
Well, maybe the switch had some crud in it and I knocked it loose taking it out. I put it back in the fan and, of course, nothing. I wondered if I was getting power to the bulbs at all... I mean, the fan runs, the bulb must have been getting power before it blew, and all the breakers looked OK...But since you never know what kind of maniac wired your house it makes sense to check all sorts of things it makes no sense at all to check, you dig?
Since the wall switch felt mechanically "fine" (not loose, good action going from up to down then back) I decided to test for power to the bulbs at the fan. With the wall switch in the OFF position I got the expected 0.0VAC. In the ON position, though, I got less than 1.0 VAC but not zero. I mean, what gives? It's a switch, some wire, another switch, and some bulbs, right?
Wrong. I didn't notice the little part (pic in the upper left of this post) that was in series with the bulbs. On the front it had the label “Y59 B 120C” and on the back it had “Limitor T160”. After some searching (I couldn’t find an exact match [9/27/15 edit: see comments for link to part]) I was able to determine that it was a thermal/current limiting switch. If its surroundings get too hot (120C) or the current gets too high (B = 5 amps, I think), the switch opens and kills power to whatever it is that is causing the issue.
Good idea, right? I guess, but in this case I'm questioning the reasoning behind installing it here.
I mean, 120C?! Yikes! This is higher than the melting point of many commercial grade plastics, but is thankfully under the melting point of PVC insulation. Based on the location of this item, the recommended max wattage of the bulbs, and the distance of the bulbs from the metal housing, things would have to be pretty bad for this tiny thing to decide that the only way to save the day is to shut off the lights while the apparently-engulfed-in-flames ceiling fan blades continue to merrily spin round and round...
I can almost hear the calliope music now.
Since the lights were off when I flipped the switch and stayed off after the remaining lightbulb popped off to join the choir invisible I was 100% sure this part did whatever it does to keep the inrush current under 5 amps while the tungsten filament vaporized (destroy itself, I guess). No heat issue. No lasting over-current issue.
After some more searching on Hunter ceiling fans I discovered that lots of people have had this problem. I also discovered that some people REALLY, REALLY hate the Hunter corporation and Home Depot. It's all "lack of customer service" this and "horribly filthy expletive deleted" that. Entertaining but not super helpful. The Limitor website seems to disavow any knowledge of that exact part number, and the closest match I could find at AllElectronics was for a normally open switch, not a normally closed one.
A couple of sites, though, said some people simply bypassed the switch and things got back to normal. The reasoning some gave for justifying the bypass was a little cavalier and/or conspiracy theory driven (ranty planned obsolescence stuff).
Normally you don't want to bypass or defeat safety devices but, in this case, I couldn't come up with a scenario where the thermal part of the switch would ever be useful. Maybe... and this is a pretty big "maybe"... if the room was already at the upper operating limit for the fan AND the bulbs inside were at or exceeded the max wattage AND the fan was not running then maybe the temperature inside the wiring housing could get to 120C, causing the switch to open in an attempt to cool down the unit. But, even then, once the unit cooled down the switch would (maybe) close and either a) arc weld itself shut or b) self destruct open.
Exactly the way a lightbulb filament fails...
So why not use a thermal fuse to begin with? Or "nothing"? Does this thing also have some surge-suppressant capability that helps extend the life of the bulbs? Maybe. If so, maybe it’s also there to extend the life of the pull-chain switch. I’m sure there is a reason I am not smart enough to understand, and I wasn't going to armchair quarterback their engineering/sales/legal decisions any further. After all, the sun was going down and you need good light to fix a light (something that totally blew my six-year-old's tiny little mind).
So in the end I cut power to the fan, snipped out the part, stripped the wires, and twisted them together with the smallest wire nut I had. I reassembled the... uhh... assembly and flipped the wall switch. After cursing profusely in the gathering darkness for a few seconds I remembered that I yanked the pull chain to the light while I was putting it back together. Dummy. Another pull and there was light.
And I saw that it was good.
I kept the two 40W incandescent bulbs shining for a few hours and "measured" the housing temperature with the back of my hand. Nice and cool.
I might someday just out of curiosity take a thermocouple and actually measure the temperature inside the housing but I probably won't. If I notice that I am going through a lot more bulbs than usual I might revisit this issue, especially if I begin blowing through the newer fancy-schmancy expensive ones. Time will tell.
All in all seems that the bypass surgery was a success - your results may vary. If you do choose to bypass the part, do yourself and your family a favor - use your brain and be careful. After all, I'm just some dude on the Internet and, as Richard Bach might say “Everything in this blog post may be wrong”.
Good luck!