Help identifying contactor terminals
I am trying to confirm which terminals are L1/L2 and T1/T2 because I probably need to replace this. I see 240V at the bottom at all times, so those terminals should be L1/L2? It seems unusual compared to the terminal locations on replacement contactors.
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L1 & L2 are the incoming power, T1 & T2 are the switched side that feeds the compressor etc. They should be marked on the contactor, usually raised in the plastic casting of the body, or printed on it.
Mechanically speaking, there isn't a difference between the T's & the L's (i.e. you could feed the T's without issue)—but there is between the 1's & the 2's. That particular contactor only switches one side, the other is an unswitched shunt pole. If your replacement contactor is the same style, you must make sure it's wired up the same so the correct leg gets switched. A true 2-pole contactor may be substituted, in which case it doesn't matter which pole is which.
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And the MFgs always bring the power in the bottom which is wrong.
And they use a single pole contactor where it should be a two pole…….that must save them at least $.10
They rail about safety and then violate what we were taught.
But, they get it passed by the know nothings at UL so it has nothing to do with the electric code.
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Thanks - that answered everything perfectly. I can't find anything stamped on this one, but in comparing to others it looks like they are using this one in reverse.
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I'd replace it with a 2 pole contactor, with that single pole contactor and terminal strip if it is connected to 240v residential power, everything inside is always live.
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But don’t both poles carry voltage? Black and red wires? If so, you’ve always got some voltage going to the compressor?
I agree: Not safe.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
some manufacturers use the winding as a crankcase heater. That requires a single pole contactor.
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You can't use the winding as a CCHtr with one pole open you have no circuit.
I think Carrier was the first one to go with SP contactors.
they talk about safety until someone blunders into live power. All so they can save a few pennies
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I’ll post the diagram.
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here’s one
I’ll get another later
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So you are calling out a safety issue if somebody were to start working on the unit without pulling the fuse to cut power?
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Yes, the entire unit is live until the disconnect is killed.
Yes, some units have the CCH across the open contacts & therefore trickle voltage thought the CCH whenever the contactor is open. It's actually pretty clever, it automagically Does The Right Thing.
It doesn't bother me, I learned decades ago to keep my li'l jammers outta equipment. Plus it doesn't hurt that much anyway.
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So the only reason that 1-pole contactors are used instead of 2-pole contactors is due to cost? There is no other reason the manufacturers spec these?
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Cost is likely the driving consideration, but if there's a crankcase heater (CCH), there's a possibility that it is dependant on that shunt pole for property operation. Look for a silver band around the bottom of the compressor, tightens with a hose clamp screw.
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Doesn't look like there's one, it would have one wire on top of the operable pole & one wire on the bottom of the operable pole.
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I don't see a wire for a crankcase heater on the line side of the contactor. Don't know why they used 10-3 for the field wiring.
There are reasons to work on it live. If the contactor is off many would be less careful about touching terminals.
If it is always live and water gets in there in the off season some current will flow and cause electrolysis. If it were dead it probably would dry out before it saw power.
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Here's an IOM for that unit. As it turns out, the CCH is only used on the 4 & 5 ton units (XC-16-48 & -60); and it's fed from the line side of the contactor & switched via a thermostat.
The schematics is on page 12, you can see how the contactor is connected.
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Your right about the CCH I was wrong. They let the CCH back feed through the compressor windings in the off cycle
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Can you show me how that happens?
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
Yellow highlight is the CCH circuit. that is turned off when the contactor closes. So adding a 2 pole contactor will disable the CCH
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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So since this is a 3 ton that won't be a problem.
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Correct—if I have the right schematic. The IOM I added is IIRC slightly newer than the unit, it's possible that the one @EdTheHeaterMan posed above is the right one for that date code, IDK.
But the pic doesn't seem to show one, whichever diagram is accurate.
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@Alan (California Radiant) Forbes
Leave it to the MFGs to come up with the screwball ideas just to screw everyone up.
I can remember when Scroll compressors first came out and the MFGs said basically " you don't need a CCH with a scroll they will eat liquid" Carrier junk was big on this. After they started replacing compressors they changed their tune
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