potential relay

Discussion in 'HVAC Heating & Cooling' started by tom-rad, Nov 14, 2013.

  1. tom-rad

    tom-rad New Member

    Messages:
    23
    Location:
    Maryland
    Can anyone tell me what would cause a potential relay to not open?
    Original issue began with chattering relay, then no startup (bad run cap found also).
    The relay has been changed, and I get 200v on the caps at startup. Bad compressor winding maybe? It's a Bryant/Carrier Two speed. Compressor runs about 10-12 seconds, then trips overload.
    Thanks.
  2. tom-rad

    tom-rad New Member

    Messages:
    23
    Location:
    Maryland
    more information


    Start cap is ok, Potential relay is new, run cap is new. 234v on contactor when compressor is running.
    I found the pick up voltage to measure only 140-200v before it shuts down, and the relay PU needs to be 295-324. The relay DO is 60-135.
    I've narrowed it down a bit, lol. Any clues? Thanks.
  3. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,351
    Location:
    Houston, TX
    Did You replace the Cap with the proper Run Cap ?

    There is a difference in run and start caps.

    Does the run winding measure good ?

    Does the new cap get hot ?


    Good Luck.
  4. tom-rad

    tom-rad New Member

    Messages:
    23
    Location:
    Maryland
    Thanks Don, the 25uf GE Genteq run cap is identical to the original, same part number also.
    I'm going to check the run winding tomorrow, got too late to work on it today.
    The new cap doesn't seem to get hot, but the unit shuts down pretty quick.
    Thanks again. Will post results if I ever get this figured out.
  5. tom-rad

    tom-rad New Member

    Messages:
    23
    Location:
    Maryland
    update - checked compressor windings

    Ok, I've narrowed this down a bit - as a matter of fact, I believe the trouble isn't electrical. I checked the compressor windings and the dc resistance is right where it should be, and with no shorts.
    Symptom:
    The compressor runs about 15 seconds before I get a thermal overload shutdown error. I also noticed that:
    1 - the compressor does not generate a high enough emf to open the potential relay;
    2 - the reversing valve does not switch, either in 'checkout' mode for a/c or heat.

    I am no expert on refrigeration, but I'm guessing either high pressure, or missing some refrigerant.
    This is a Bristol two speed (Bryant 698B, from 2005 heat pump) compressor, with R410A , or Puron. Anyone have any ideas? And, as I mentioned, I'm out of work, so have to do as much as I can myself. Thanks.
    Last edited: Nov 20, 2013
  6. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,351
    Location:
    Houston, TX
    Is that new relay made for your compressor ?

    Maybe try the old relay ? If the cap was bad then the old relay may be OK.

    If the compressor never comes out of start maybe the compressor could have a mechanical problem.

    A amp probe would be a good tool to pin the problem down.


    Good Luck.
  7. tom-rad

    tom-rad New Member

    Messages:
    23
    Location:
    Maryland
    thanks for the reply

    Yes, identical relay, same part number. Same symptoms with both old and new relay.
    Don't have a clamp-on ammeter right now, but considering the drop of about 6v under load, I believe the compressor is ok electrically.
    Weather has been mild, but over the weekend it's going to get colder. May have to get a loan and call the local Carrier service tech.
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