Page 2 of 3 FirstFirst 123 LastLast
Results 14 to 26 of 31
  1. #14
    Join Date
    Oct 2008
    Location
    mid-Tennessee
    Posts
    691
    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.

  2. #15
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,220
    Why is a million ohms from winding to ground a problem?

  3. #16
    Join Date
    Jun 2013
    Location
    N. Canada
    Posts
    368
    Quote Originally Posted by hurtinhvac View Post
    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.

  4. #17
    Join Date
    Oct 2008
    Location
    mid-Tennessee
    Posts
    691
    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.

  5. #18
    Join Date
    Oct 2010
    Location
    AZ
    Posts
    635
    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"

  6. #19
    Join Date
    Jan 2007
    Location
    Stongsville Oh
    Posts
    893
    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.
    ckartson
    I didn't write the book I just read it!

  7. #20
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,907
    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.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

    AOP Forum Rules:







  8. #21
    Join Date
    Jul 2005
    Posts
    5,365
    Quote Originally Posted by hurtinhvac View Post
    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.

  9. #22
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    1,989
    Thanks for all the responses guys. As I dig further into this I will keep you posted.

  10. #23
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,220
    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.

  11. #24
    Join Date
    Jul 2013
    Location
    Harrisburg, PA
    Posts
    281
    Quote Originally Posted by hurtinhvac View Post
    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

  12. #25
    Join Date
    Nov 2011
    Location
    St. Louis
    Posts
    3,220
    Quote Originally Posted by CoolShowers View Post
    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.

  13. #26
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    1,989
    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.

Page 2 of 3 FirstFirst 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event