A/C Contactor: Single Pole vs. Double Pole?


  #1  
Old 06-04-24, 01:39 PM
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A/C Contactor: Single Pole vs. Double Pole?

Doing some PM on my 13-Yr-Old Lennox 4-Ton, replacing dual-run cap and contactor. (Herm is weak, contactor works fine AFAIK, but at 13 years age, might as well replace.) Looking online for "Definite Purpose Relays for A/C," there seems to be an equal offering for both single pole and double pole units. I ordered a double pole, assuming that's what it had, but upon closer inspection, discovered it is a single pole. Thinking that a double pole would be "safer", that is, when it's off, there's no hot load side that could fault to ground, I'd just go ahead and use that one. Noticing that the relay specs all have the contacts/voltage ratings, but no coil resistance rating, after receiving the new relay, I checked and discovered the new double pole relay coil shows 13 Ohms, but the old single pole shows 18 Ohms, which means the double pole will draw significantly more current, and possibly run hotter. That was somewhat concerning, so I ordered and just received a new single pole, and it measures 17.5 Ohms, so I'll use this one.

So after all that explanation, why do some A/C units use double and some single pole?
 
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Old 06-04-24, 02:24 PM
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When replacing a contractor.... you should match the old one.
Single or dual pole.
Sometimes a single pole contactor is used if it supplies a crankcase heater.
They are all 240v contactors. That can be one pole or two pole switched.
I will only replace like for like.
If it's one pole switched..... use that type.
 
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Old 06-04-24, 06:49 PM
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Thx PJ, it does indeed have a thermostatically-controlled heater, but it's a 240V heater wired across the line side of the contactor, and so is always hot, as long as the A/C breaker is on.
 
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Old 06-04-24, 06:51 PM
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Then you could use either type.
 
 

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