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Current relay/potential relay

Harvey Ramer
Harvey Ramer Member Posts: 2,261
in A-C, Heat Pumps & Refrigeration
How best to test these miserable critters while the compressor is dry docked? Don't want to be wasting any start caps.



Harvey

Comments

  • Eugene_Silberstein
    Eugene_Silberstein Member Posts: 349
    Checking PMRs and CMRs

    Checking a Current Magnetic Relay:



    Take a resistance reading across the coil on the relay (usually terminals L and M) - The resistance of the coil should be less than 1 ohm or so.



    Position the CMR in its normal position (coil at the bottom) and check for continuity across the contacts of the relay (Terminals S and L). This reading should be infinite. Now, with the meter's leads still connected to S and L, turn the relay upside down. You should now read continuity. This indicates that the contacts are moving freely within the relay.



    If the coil and the contacts check out, the relay is good.



    Checking a Potential Magnetic Relay:



    Take a resistance reading across the coil (terminals 2 and 5) on the relay - The resistance of the coil should be very high. This resistance varies from manufacturer to manufacturer, but readings well above 1000 ohms are common.



    Next, check for continuity across the contacts of the relay (Terminals 1 and 2). This reading should be zero or very close to zero.



    If the coil and the contacts check out okay, there is still the possibility that the relay is not functioning properly. You still need to check whether or not the contacts open when the "pick-up" voltage is reached. The pick-up voltage is the voltage at which the contacts will open, and is much higher than the line voltage that is supplied to the unit.





    I hope this helps!

    There was an error rendering this rich post.

  • Techman
    Techman Member Posts: 2,144
    Pot Relay

    .I always visually check the contacts of the Potential Relay. The new PR is easy to gain access to the contacts, the older PR has a screw on the backside ,under a piece of dried up rubber.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,261
    It certainly does.

    Thanks for the help guys!!!



    Harvey
  • don_9
    don_9 Member Posts: 395
    Very rare

    For that relay to go bad. If the comp is locked you can always piggy back a booster on the run capacitor. If relay is working it is taking out the start winding. Keep in mind with no power to the start winding it will give you the reading on your meter like a locked comp would.

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