Post a reply to the thread: Compressor reads like a capacitor?
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wow! for a moment -tought U wuz channelin phd, I mean phm channelin my last post!
Sorry guys, my typing is poor, that's what happens when I let my phone do the typing. It was supposed to read " talk to the customer about more testing or replacement."
Originally Posted by Poodle Head Mikey Isn't that just the opposite of a Starboardcastle Replacement? PHM ------ Lol! XD
Isn't that just the opposite of a Starboardcastle Replacement? PHM ------ Originally Posted by ckartson What is a Portcastle replacement
What is a Portcastle replacement
Talk to the homeowner about Portcastle replacement, they decided not to put any more money into it and just change it out. We took about twice as much refrigerant out as what it actually needed. When we got back to the shop I reject the compressor. Resistance checks tests okay. So maybe it was just the excessive amount of refrigerant that was in it.
Originally Posted by CoolShowers Loose spade connectors I've heard can fry wires like that. I've seen a couple units where the wire from common terminal on the cap got fried going to the contactor. Fan kicks on and off, but no compressor turn over. Also, how did you not see the fried wire before checking voltages? :P Spade connector at run tap on compressor...not contactor. And the spade wasn't loose, it stayed on after the wire broke loose - had to yank it off with needle nose. Noticed a newer run cap with a mile of electrical tape on the terminals just sitting there in the panel. I'm starting to wonder if the thousands of cap changes in last years blistering heat will give way to bad CF motors, crispy high resistant wires and toasty contactors during this years periodic hot and wet spells. It was low nineties but extremely wet today.
Originally Posted by hurtinhvac Sure enough, first call out of the gate this morning the compressor isn't turning over. Fan is going strong. Cap looks fine, check it and incoming voltage real quick and move on to removing the compressor leads. Common to start, 2.9 or so; common to run, 1 point something million. Well, hello there...nice to meet you so soon! Just a crispy wire and spade connector at the run tap, cause unkown, no suspects willing to show themselves. Before I buttoned everything up to fire it and try to get a handle on the cause; I ohm each winding against each other and ground..Each winding got 30 something million to ground. This is with a Fluke 116. So yeah...I'm thinking I'm much more comfortable with 30 million to ground as opposed to just one and change. Loose spade connectors I've heard can fry wires like that. I've seen a couple units where the wire from common terminal on the cap got fried going to the contactor. Fan kicks on and off, but no compressor turn over. Also, how did you not see the fried wire before checking voltages? :P
Sure enough, first call out of the gate this morning the compressor isn't turning over. Fan is going strong. Cap looks fine, check it and incoming voltage real quick and move on to removing the compressor leads. Common to start, 2.9 or so; common to run, 1 point something million. Well, hello there...nice to meet you so soon! Just a crispy wire and spade connector at the run tap, cause unkown, no suspects willing to show themselves. Before I buttoned everything up to fire it and try to get a handle on the cause; I ohm each winding against each other and ground..Each winding got 30 something million to ground. This is with a Fluke 116. So yeah...I'm thinking I'm much more comfortable with 30 million to ground as opposed to just one and change.
Thanks for all the responses guys. As I dig further into this I will keep you posted.
Originally Posted by hurtinhvac Why is a million ohms from winding to ground a problem? It isn't, but it is an indication of contaminated oil. Still not enough leakage to ground to even worry about, but what caused the contamination? My guess in this case is a loop to loop short. I've run across the exact same situation several times over the last 30 years. FWIW you don't need a megger to test the prevailing theory here. Just disconnect the run lead from the contactor, reset the power and energize the contactor. On three phase just disconnect two of the leads. With one leg being fed to the compressor you now have line voltage to the windings, and a supposed short to ground under line voltage will show itself. If the fuse doesn't blow or the breaker doesn't trip, then you know a short to ground isn't what's tripping it. It also isn't due to a locked rotor, since by design the breaker/fuse isn't supposed to instantly trip under locked rotor. If it did you'd be resetting/replacing them every time the compressor tried to start under normal operation.
I meg is not enough. When the power is applied, this resistance can drop, because it is a resistance based on the response to a 9vdc powered circuit.
I consider readings less than 30 meg poor. I would try a megohm meter although the fluke you are using is a good meter you might get a consistent reading with a meger. The system may run and just need cleanup. Evac and oversized driers. One meg would not be acceptable and I would not be surprised that it blew fuses.
Just because you test windings as being ok with a standard meter doesn't mean they are ok. Standard ohmmeters put a small voltage across the windings but when the motor runs, they have a much higher voltage across them. Could be if you connected a megger, which puts a much larger voltage across the windings, they wouldn't pass the test. If the insulation has been breaking down over the years, it may be able to insulate the 1.5 volts or whatever the meter is putting on it but not the 240 or whatever line voltage is. If you want to find out if the problem is electrical, find someone with a "megger" aka "megaohmmeter"
You guys may know more about the website in this link than I do. Here's an article on the subject: http://www.hvacexams.net/articles.php The operative phrase in this article is the last sentence in the first paragraph when mentioning "associated voltage." * * * HINT>> Hit the mute button to kill the dayum "Predator" soundtrack noise.
Originally Posted by hurtinhvac Why is a million ohms from winding to ground a problem? Like ECtofix post says, an applied voltage of 9 volts tells you nothing about insulation breakdown and arc-over at 230v. Not sure if a megger is much better with a single reading (Copeland condemns 《 .5meg) A hi-pot tester that monitors current leakage (used by Copeland and U.L. testers) will give the definitive answer which probably be to change it.
Why is a million ohms from winding to ground a problem?
I agree that the compressor is at fault - by your process of elimination. Whatever happened inside that compressor was electrically catastrophic. There's no way of knowing what type/form of physical damage it took on, so I can't offer any explanation. It's enclosing a fifty year old mix of oil, possible acid and moisture to go along with its revealed insulation failure. That Fluke 289 looks like some fancy gadget compared to my 116. However, it doesn't look like it has a "megger" feature on it. So, it can only provide a little 9 volt battery, which is a pittance of force to push through an insulation failure if that failure is "iffy". Yet, it still gave you that initial 1 MΩ reading and is a sure sign of a problem. Obviously the 208 volt source power pushes through the problem far more easily - enough to blow fuses. I'm sure a megger would also expose the problem quite readily as well.
I don't disagree at all that any significant repairs to a '65 system is likely unwise. I was born in '65 and I'd have to think about any significant repairs to myself. I'm sure my wife would opt for a new unit; even if she could get a pump on the side for cheap. Hell I'd urge replacing a 48 year old system even if it was working ok. Again, so would my wife. I only raised an eyebrow over the ohm readings. Assuming incoming voltage is within 10% of data plate: A million ohms from winding to ground would indicate that the winding is not shorted to ground. The old RSES ROT is anything over 1k ohms per volt is passable. At 240 volts give or take, and 1k per; the compressor would pass the short to ground test at a quarter of a million ohms from winding to ground. If there is measurable resistance from common to run and common to start, and start to common is 3-6 times as much as the run winding it would pass the winding to winding, shorted and open winding tests. Which leaves mechanical failure. The two most common causes of breakers or fuses tripped immediately upon start up are windings shorted to ground and mechanical lock up. An amp clamp on the start winding might not be fast enough to catch it if it's blowing right away. But I'd hazard the latter based on the resistance readings you provided. That said, I just read an entry in the MSAC technical Q&A of the July RSES mgazine. The tech replaced a Carlyle compressor in a Flotronic chiller and it blew up the contactor in a few days. He got the replacement compressor, took the resistance readings and they were identical to the suspect compressor. So he just changed the breaker and the contactor - which he pushed in with a 4' pole and it immediately blew up. He then went ahead and changed the compressor and everything ran fine. So if incoming voltage is within spec, winding to winding and winding to ground all check ok, and all wiring to and from is corrosion free and not providing any meaningful resistance...it has to be mechanical seizure of some nature. Right? I'm really asking...not telling.
With the compressor in the circuit it will clear the fuse before the fan can start. Take the compressor out of the circuit and the fan runs fine. If it's not the compressor what is it? That's the only component in the system that even shows any kind of reading to ground. We're talking simple 1965 A/C, compressor, fan, 2 run caps, and a contactor. Even if the readings are suspect the process of elimination says the compressor is bad. On a unit this old is it really worth recovering the refrigerant, pulling a vacuum while heating the compressor, putting in filter driers assuming moisture and then recharge with fresh R-22 so as not to re-introduce moisture. And that's not counting doing the repair for why refrigerant was added in the first place. There either has to be a leak or a restriction i.e. bad TXV, plugged cap tubes, etc. I don't know why refrigerant was added in the first place, the owners of the rental said they didn't think he knew what he was doing. I don't know who it was and really don't care. The thing is broke now and the cost of digging into this thing would mean putting a lot of money into an old unit that's seen better days.
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