Results 1 to 9 of 9
  1. #1
    Join Date
    May 2012
    Location
    NC
    Posts
    56

    Could under sized cap cause a wire to blow off

    Two questions just for my curiosity.
    Here's what I found. Customer moved in Saturday, claimed it worked Sunday and Monday. No cooling on Tuesday.
    Lennox 10ACB48-10P outdoor unit, 4 ton cool only not running, contactor pulled in calling for cool. Capacitor had blown its white and grey waxy "guts" everywhere. Breaker tripped.
    I tested for the proper ohms through common, start and run and got the proper readings. I can't remember them but they were correct. I also checked for short to ground. No short found.I replaced the capacitor,35/5, and restored power. Breaker immediately tripped and I heard a pop from unit near/under compressor. I then found the common disconnected from the compressor(source of the pop) and two different brand "stake on" connectors on start and run. Terminals old and dirty but not deformed to much. This unit appears to have been band aided for a while.

    Lennox calls for a 50/7.5 capacitor. I'm returning and installing another stake on and the proper size capacitor. I'm replacing the other two old stake ons too if needed.
    1. Is there any way a compressor/fan rated for 50/7.5 ever ran on a 35/5?
    2. Did the wrong size capacitor have anything to do with the wiring issue? Would it overheat the connection and cause it to fail? Could an under sized capacitor cause the wire to blow off its terminal? (ok 4 questions)

  2. #2
    Join Date
    Jul 2005
    Posts
    5,576
    Quote Originally Posted by alamo1718 View Post
    Two questions just for my curiosity.
    Here's what I found. Customer moved in Saturday, claimed it worked Sunday and Monday. No cooling on Tuesday.
    Lennox 10ACB48-10P outdoor unit, 4 ton cool only not running, contactor pulled in calling for cool. Capacitor had blown its white and grey waxy "guts" everywhere. Breaker tripped.
    I tested for the proper ohms through common, start and run and got the proper readings. I can't remember them but they were correct. I also checked for short to ground. No short found.I replaced the capacitor,35/5, and restored power. Breaker immediately tripped and I heard a pop from unit near/under compressor. I then found the common disconnected from the compressor(source of the pop) and two different brand "stake on" connectors on start and run. Terminals old and dirty but not deformed to much. This unit appears to have been band aided for a while.

    Lennox calls for a 50/7.5 capacitor. I'm returning and installing another stake on and the proper size capacitor. I'm replacing the other two old stake ons too if needed.
    1. Is there any way a compressor/fan rated for 50/7.5 ever ran on a 35/5?
    2. Did the wrong size capacitor have anything to do with the wiring issue? Would it overheat the connection and cause it to fail? Could an under sized capacitor cause the wire to blow off its terminal? (ok 4 questions)
    A smaller capacitor results in lower amperage through the capacitor and lower voltage across the capacitor, so the short answer is no. Burned connections are almost always due to a poor/resistive connection.

  3. #3
    Join Date
    Apr 2010
    Posts
    93
    Yes, the unit could've ran on a 35/5. And yeah as he said ^ Poor connections are usually to blame. Also, high starting amperage will not help the situation. Although, I read your post again and it sounds as if you came across the unit with the breaker tripped and exploded capacitor, replaced cap, then tested, breaker tripped again and this time you found the connection blown off common, after you'd performed the omh test? I think you may have a failed compressor, or another issue on your hands. Not doubting your troubleshooting capability, but I wouldn't be surprised if upon return the breaker trips again. Report back, and good luck... I would bring a hard start kit with me if I were you. Hard start - not a "soft" start.

  4. #4
    Join Date
    May 2012
    Location
    NC
    Posts
    56
    Good call Comfortablynumb, compressor locked up. After I repaired enough wire to to try to start the compressor, it tripped the 50A breaker. First time ran for a second then tripped.
    Still good ohm's, so I installed hard start. Tripped breaker again.
    Disconnected compressor from contactor,Ran fan only, didn't trip.
    Tech support agrees, compressor locked up.

    What is the difference between a hard start and a "soft" start?
    What i used and call a hard start is I believe a Supco, hard start/relay, rated to 120,000 BTU's.

  5. #5
    Join Date
    Apr 2010
    Posts
    93
    Nice. Just curious, did you have your amp probe on the unit during testing? I'm guessing your amps were somewhere around your LRA.

    "Soft" start is a piece of crap hard start kit. I believe the Supco model rated to "120,000" BTU is the SPP6E? If so, that model is worthless IMO. Supposedly rated 1-10hp I believe? Rarely have I seen that model reduce starting amperage, never unlock a compressor. Which is a crapshoot anyways. The SPP8E is a better unit. Rated for 1/2 to 5hp. Make sense of that one? Tomorrow I could get brand and part #s of some dependable kits that will actually reduce starting amperage everytime, also some that give you the best shot of bringing back a locked compressor.

  6. #6
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,777
    Quote Originally Posted by ComfortablyNumb View Post
    Nice. Just curious, did you have your amp probe on the unit during testing? I'm guessing your amps were somewhere around your LRA.

    "Soft" start is a piece of crap hard start kit. I believe the Supco model rated to "120,000" BTU is the SPP6E? If so, that model is worthless IMO. Supposedly rated 1-10hp I believe? Rarely have I seen that model reduce starting amperage, never unlock a compressor. Which is a crapshoot anyways. The SPP8E is a better unit. Rated for 1/2 to 5hp. Make sense of that one? Tomorrow I could get brand and part #s of some dependable kits that will actually reduce starting amperage everytime, also some that give you the best shot of bringing back a locked compressor.
    Hard start kits don't reduce starting amp draw. they do reduce the time that the compressor is drawing that amperage.

    Most meters don't respond fast enough to show the actual amp draw with a good stat kit. Which is why so many think it prevents the compressor from drawing as many amps on start up.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    May 2012
    Location
    NC
    Posts
    56
    I put my amprobe on during testing. I tried three times. The breaker tripped so fast I couldn't get a reading, even when I set it on "max".
    The disconnect was 1 foot from away from the service panel, the old capacitor blew in the direction of the disconnect and the compressor terminals were pointing at the disconnect. I was there by myself. If anything went bad violently/quickly it was coming my way. After three tries at an LRA, tech support and I agreed on a bad compressor.

    "Hard start kits don't reduce starting amp draw. they do reduce the time that the compressor is drawing that amperage." beenthere

    How do they reduce the time that a compressor is drawing that amperage? I think I understand that the compressor needs a certain amount of "amps" to start but I can't get my head around how it does it quicker.

  8. #8
    Join Date
    May 2005
    Location
    South
    Posts
    580
    Quote Originally Posted by alamo1718 View Post
    . After three tries at an LRA, tech support and I agreed on a bad compressor.
    You had to call tech support for that?
    How about an ohm test on the compressor?
    If it ohms out ok, all the wires are connected properly in the right places then it's mechanically locked.

    At any rate if it trips the breaker that fast you can damn sure bet it's bad. Would be pretty odd if it was something else.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,777
    Quote Originally Posted by alamo1718 View Post
    I put my amprobe on during testing. I tried three times. The breaker tripped so fast I couldn't get a reading, even when I set it on "max".
    The disconnect was 1 foot from away from the service panel, the old capacitor blew in the direction of the disconnect and the compressor terminals were pointing at the disconnect. I was there by myself. If anything went bad violently/quickly it was coming my way. After three tries at an LRA, tech support and I agreed on a bad compressor.

    "Hard start kits don't reduce starting amp draw. they do reduce the time that the compressor is drawing that amperage." beenthere

    How do they reduce the time that a compressor is drawing that amperage? I think I understand that the compressor needs a certain amount of "amps" to start but I can't get my head around how it does it quicker.
    By providing more power to start the compressor. Gets the compressor up to speed quicker.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

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