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Old 11-03-13, 07:25 AM
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Reading '

Part # on side of this fan relay: 42-21571-01, for a Rheem 15KW Electric
Furnace.

This olive-colored pic of the relay is supposed to be the same part # as above. I'm aware that online pics are sometimes substituted when the exact pic is not available. The difference here is.... on the actual relay, the flat part of the quick disconnect (#4) laying flush against the relay body covers a larger area, as in the red rectangle I've added. I guess that makes sense, because that would give continuity to #4 & #6 as is shown in the diagram (#6 is not labeled in the diagram, as it is also not labeled on the actual part diagram, but it is shown on the olive-colored pic).

The relay diagram is shown with the coil energized, resulting in continuity between #4, #6 & #5 ? If that's correct, what happens when the coil is de-engergized... the other side of the movable contacts with the half circles, make contact with #4 & #2 ?

What the two bare metal posts recessed in the bosses for? Test points?
 
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Old 11-03-13, 07:42 AM
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Your picture did not post but that looks like a standard single pole double throw relay with a 24 volt coil.
 
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Old 11-03-13, 07:45 AM
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That relay is called a SPDT type. Ignore the terminal #6 as it only adds confusion to the mix.
Terminals 1 and 3 are the coil
Terminals 4 and 5 are normally closed
Terminals 4 and 2 are normally open

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I don't know what the recessed posts under the relay are for.
 
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Old 11-04-13, 06:25 PM
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I thought normally closed meant no power applied to the coil (in this case, since NO or NC is not marked anywhere). Not so?
 
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Old 11-04-13, 07:25 PM
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A closed circuit will pass current.
An open circuit will not pass current.
 
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Old 11-04-13, 09:01 PM
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plumducy
I thought normally closed meant no power applied to the coil (in this case, since NO or NC is not marked anywhere). Not so?
Okay, I mis-spoke there, and one more question should clear it up for me... Is the diagram in PJ's pic showing the coil energized or de-energized?

And I'm assuming that the two bars with the half-circles at their ends are a movable set of contact points (responding to the coil's magnetic field), which are physically connected, but not electrically of course.
 
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Old 11-04-13, 09:06 PM
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The coil is not energized. The diagram on a relay is always at it's non powered state.
The two bars is the plate that moves with the contacts on them.

That diagram I posted is right from the side of the relay. Most relays either have a diagram like that on them or the contacts are marked as common, NO and NC.
 
 

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