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  1. #1
    Join Date
    Jul 2008
    Posts
    440

    Blowing start caps WHY OH WHY

    Title a little more dramatic than need be. Went on call other day- dual evap med temp walk in froze up. Made few observations. We just took cust from another company. first off cycle timer not even in circuit 2nd and most contributing factor 2 out of 3 fan motors wrong rotation. Before installing correct motors I defrosted with hot water like i usually do when its an option. After enabling unit cleaned up and something didnt seem right Went on roof checked unit and sure thing comp short cycling on overload. Found start cap no good. There was a hole in the rubber membrne but no charring or debris. Relaced start components and she took right off. Cap and relay had just been replaced in March per date. Question is could starting against an abnormally heavy load (from the hot water) had played a role in blowing start cap? There is no CPR as its medium temp. What kind of factors contribute to cap and other component failure?
    "It's just like it doesn't work. I mean it seems to be ok now, but it usually like never works"

    "Never an always and always a maybe"

  2. #2
    Join Date
    Oct 2010
    Location
    SW Michigan, near Battle Creek
    Posts
    921
    I think power fluctuations kill capacitos.

  3. #3
    Join Date
    Jul 2008
    Posts
    440
    I agree however in this case it was running fine an hour prior to doing my work inside the box. Nice trying to explian that one.
    "It's just like it doesn't work. I mean it seems to be ok now, but it usually like never works"

    "Never an always and always a maybe"

  4. #4
    Join Date
    Aug 2009
    Location
    Bracebridge, ON
    Posts
    73
    I would be looking at the potential relay, that is usually what causes SC to blow.

  5. #5
    Join Date
    Oct 2010
    Location
    SW Michigan, near Battle Creek
    Posts
    921
    yeah the relay hangs up and boom. makes sense to me.

  6. #6
    Join Date
    Apr 2010
    Location
    southern california
    Posts
    535
    Low voltage condition,defective potential relay,drop out voltage to high, compressor winding values have changed.

  7. #7
    Join Date
    Jul 2002
    Location
    Yuma, AZ
    Posts
    2,361

    Trust No One.

    Quote Originally Posted by dave1234 View Post
    ...Cap and relay had just been replaced in March per date. ..
    1. Most likely the relay is a less than perfect replacement choice. OEM is best.
    2. Never hurts to go back to the manufacturer's specs for both start cap and relay.
    3. Also check the running capacitor if it has one.
    "I have never let my schooling interfere with my education."
    Mark Twain
    More at: http://www.quotationspage.com/subjects/education/

  8. #8
    Join Date
    Mar 2004
    Location
    Las Vegas, Nevada
    Posts
    1,647
    Gotta go with Lynn on this one. Also, many SCs come with Bleed Resisters, but they can be purchased separately if not included. I'm a bit weak on my single phase, but the bleed resister does seem to help the Start Kit live a lot longer. Hope that helps.
    The views and opinions posted here are my own. They do not reflect the corporate policies of my employer and will most likely get me fired at some point.

  9. #9
    Join Date
    Jul 2008
    Posts
    440
    Actually yes the pot relay was an aftermarket. In this case I replaced all 3 components with OEM parts. If memory serves the contacts on a pot relay are between 2 and 5 and are ... ... N.C (? cant remember if theyre NC or NO and I know a current relay is the opposite regarding the contacts. I have never seen a pot relay with the pick up voltage rating on it so you do you guys troubleshoot starting relays. So a start cap that stays in the circuit to long can go then i take it. Strange usually I see them blown up on end or expanded or guts all over- but not always the case I guess.
    "It's just like it doesn't work. I mean it seems to be ok now, but it usually like never works"

    "Never an always and always a maybe"

  10. #10
    Join Date
    Sep 2008
    Location
    Vancouver , BC
    Posts
    293
    potential relay 2 and 5 is coil and between 1 and 2 is NC

  11. #11
    Join Date
    Feb 2009
    Posts
    139
    Iced evap causes short cycling caps rated for starts per hour. short cycling a common cause

  12. #12
    Join Date
    Jul 2002
    Location
    Yuma, AZ
    Posts
    2,361
    Oops.
    "I have never let my schooling interfere with my education."
    Mark Twain
    More at: http://www.quotationspage.com/subjects/education/

  13. #13
    Join Date
    Dec 2011
    Location
    USA
    Posts
    66
    Please check the voltage rating on the cap. It should be greater than the voltage to the compressor. Example if the compressor is 220V then the cap should be say a 330V.

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