Help me understand this relay please

markiz41 · Apr 19, 2016

It's a motor control relay, the sort that performs the function of a centrifugal switch. The small coil, when energized, is supposed to draw in this magnet and separate the contacts that control the start windings. Apparently, it isn't doing that, the motor can't get going at full speed. I took the relay out and the coil shows no continuity. However, when I apply 120V to it, it buzzes and the meter shows correct voltage.. how's that possible? A short somewhere? Contacts still do not open with the voltage present. Thanks for any insight.

Bob · Apr 19, 2016

What are you working with? A hermetic refrigeration compressor, for example?

There's two types of those relays... the current type, where high run winding current at startup causes a CURRENT RELAY to close and power the start windings, and a POTENTIAL RELAY, it's contacts are already closed when power is put to the motor, when the motor comes up to speed the VOLTAGE (potential) across it's coil changes, opening the start contacts.

Do you know which type you are working with?

A photo would be GREAT.

http://www.achrnews.com/articles/92424-know-your-potential-starting-relays

http://www.achrnews.com/articles/98936-current-starting-relays

old · Apr 19, 2016

What scale on the ohm meter are you using?? It could still conduct power but have such a high ohm value that it does not work. Also is the part of the relay that moves free to move or have the point welded up on it which would also cause a problem like you have

markiz41 · Apr 19, 2016

It is a refrigeration pump, Bob. Looks a potential relay, since the contacts are NC..

The relay # is 128146-1613MK
128146 1613MK

markiz41 · Apr 19, 2016

Yeah, you were right. Once I set the meter to kilo-ohms, it showed resistance in the coil. Still not popping contacts open.

old · Apr 19, 2016

If you can check the contacts and make sure they're not welded up because if they are no way it can pop them open

Ranchingelec · Apr 19, 2016

Some of these relays are gravity sensitive. They will not work upsidown. Learned that lesson the hard way burning out good start windings in a sander motor.
Ranch

Bob · Apr 19, 2016

There's a pretty good chance the motor has issues/shorted windings/whatever, and the potential relay isn't seeing the voltage it needs to drop out the start winding.

markiz41 · Apr 20, 2016

Just an update. The relay works after a bit of cleaning and filing, but it's very intermittent. At least now I know that's where the problem is. Thanks for all advice, guys.

da.bees · Apr 21, 2016

Bob is right,the motor and/or capicator may be the problem. In decades of hvac,I saw 100 bad capicators for 1 bad relay.

Help me understand this relay please

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