Quick Q on stalled A/C compressor


Awl--
Actually stalled dehumidifier compressor. Turn it on, you hear the "starter circuit" buzz, lites dim momentarily, then the attempt to start goes off. ie, compressor don't kick in. I think it tries again by itself, then goes off. Capacitor?? Frozen compressor? Sumpn else? Anything I can jump out to get it going? TIA.
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Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
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browse this: http://applianceguru.com/search.php?s=1&q=dehumidifier+compressor .+
Proctologically Violated©® wrote:

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Very interesting site! Quite the link for all the appliance-related Qs in this group. Thanks!
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Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
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It very well could be a bad capacitor. More likely (these days) is a bad PTC starter (positive thermal coefficient resistor). They tend to fail long before any of the mechanics or other electrical components do.
If that's what's bad, you'll play hell buying a new one -- they're expensive and hard to acquire from the manufacturers. But you can rip one out of a junked fridge. If you're up to it, try to find an older-style current relay to replace it with.
Check the cap first, since it's the easier one to test, then on to the PTC or start relay.
If it's not one of those, it might be a locked rotor. Sometimes that can be freed by briefly substituting a dead short for the start cap. Just 'ring' it with a short BLIP of power. It's an aggressive, potentially damaging strategy, but a last-resort thing to try. If you have a locked rotor, likely it will return some time soon.
I've freed up locked rotors in units as small as 'dorm' fridges, and as large as 4-ton ACs. But it usually lasts only a few hours to days to a week before the mechanical problem that caused it overcomes the fix.
LLoyd
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What does this ptc look like? Ar ethese ptc's also in the "modern" plastic 3-speed fans? In these, it looks like a diode. Whatever it is, it used to be shoved up against the metal motor housing, now *buried* in the wires attached to the windings *inside* the motor housing.
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Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
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No, that is a thermal-overload switch.
The PTC is a nickel-sized disk of what looks like compressed fine black sand, with a contact on either face: those may consist of plating and solder, or two spring-loaded compression plates. It's usually hidden inside a bakelite or other plastic cover -- sometimes even part of a socket assembly that plugs directly onto the hermetic feed-throughs on the side of the compressor.
It works by offering a very low resistance to current when cool, so the capacitor is basically "switched in". Then it quickly heats up, and its resistance rises to a high value, limiting the current through the cap; essentially switching it out.
They degrade with time, and begin to crumble. Once the disk breaks, it may continue to work, if it's mounted between contact disks... but usually the contacts are soldered onto an area of plating on each face. When that's the case, a crack condemns the resistor.
The manufacturers don't WANT you to replace this item. So even though PTCs are inexpensive (they are often used in the degaussing circuit of color TVs), the specific value and physical size necessary to work in this application is almost un-obtainium. If you can find one, you'll find the price up in the $30 range. Not worth it, when you can rip another out of a junked unit, or better, find one of the vertical-format current-actuated relays they USED to use, until they found out they last too long.
LLoyd
LLoyd
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I've seen this! It seems, tho, to be in series w/ the whole motor, not just the cap, so that if it goes, there should be *nothing*. Or so it seemed. Can you still get that "stall" sound when these things go?
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Sure! The motor is attempting to start without the out-of-phase start winding to kick it around. It buzzes at high current until its thermal overload switch kicks it off.
(the PTC isn't in series with the whole motor, just the start winding.)
LLoyd
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Bless you. I'll be giving this a shot, later. Hopefully, GE/China stuff can be taken apart w/o destroying the g-d unit. :(
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Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
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Proctologically Violated©® wrote:

Nope. That's what you call a thermal cut-off. If it's a little square thing, good luck finding one. I have a nice quiet fan (dead now) that needs one. Also a VERY nice Klipsch subwoofer with one (dead) that was in the windings of the power transformer. I'm not gonna pay big bucks to replace the transformer from Klipsch, when all it needs is a 29 cent item. H134 thermal cut-off for the sub, H115 for the fan, if anyone knows where to get them.

PV'ing our possessions now.
in the wires attached to the

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snipped-for-privacy@verizonwallet.net (remove wallet to reply)
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Many electronic component distributors have thermal cut-outs, available as either thermal fuses or self-resetting thermal switches (thermal protection). The fuse types are also used in various kinds of small appliances such as coffee machines.
Many small motors such as fan motors, have self-resetting thermal protectors to switch off the AC power if the motor reaches a certain temperature, before the insulation temp rating becomes compromised. Additionally, many small AC motors may also have been designed with impedance protection.
Transformers (power types) typically have thermal fuse protection. These non-resetting devices are sometimes fitted into a cavity in the coil form, and might not be easily replaced.
Both of the thermal protection devices are primarily intended to be safety devices, to prevent the possibility of fires from overheated windings or heating elements.
WB metalworking projects http://www.kwagmire.com/metal_proj.html ...........
Steve Walker wrote:

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Or "thermal fuse" sometimes also in different form factors. I've purchased them in the past from allelectronics.com (but they don't seem to have any currently).
Also see "thermal breaker" or "thermal switch". Just search allectronics.com for 'thermal'.
I've also purchased thermal fuses from other places in the past, but don't remember who ATM. mpja? mcmelectronics? grainger? mcmaster? jameco? digikey? mouser? goldmine-elec? hosfelt?
Of course, if you google "thermal fuse" you will find a bunch.
sdb
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With a stalled A/C compressor, the first thing is to check the capacitor for short or open. Replace the capacitor, they are fairly cheap.
If you want dehumidifier advice, you'll have to ask for it under a proper subject line.
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Christopher A. Young
You can\'t shout down a troll.
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Proctologically Violated©® posted for all of us...

-- Tekkie Don't bother to thank me, I do this as a public service.
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Who/what is this asshole?
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Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
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Proctologically Violated©® posted for all of us...

Why that would be Proctologically Violated©® of course

-- Tekkie Don't bother to thank me, I do this as a public service.
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Why do you post here, or anywhere for that matter? What purpose do you serve?
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Mr. P.V.\'d (formerly Droll Troll), Yonkers, NY
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Proctologically Violated©® posted for all of us...

#2 To keep dufus' like you doing a little research instead of just jabbering away.
#3 I don't think I can ever explain it to a dufus like you so I won't.
#4 I get great amusement from dufus' like you. -- Tekkie Don't bother to thank me, I do this as a public service.
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