Just had a coworkers ask me about a contactor on an hvac unit , when he checks voltage on both the contactors for the blower and condensor he gets voltage on both sides of the contactor wether it is open or closed, but nothing will run unless the contactor is closed. Anyone know why there would be voltage when the contactor is open?
hvac contactor
- Thread starter mmas0n
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If i am not mistaken, (have been will be again), on one side of contact/relay its fed through, only one leg of the circuit is "switched" using the contact/relay,
the line that is fed through will go through the condenser, and the fan back to the opposite side of the contact/relay, thus giving a voltage reading on both sides
maybe i should have asked first ... was he checking line to ground? ask him to try checking 240v line to line he might just find a 0 reading
the line that is fed through will go through the condenser, and the fan back to the opposite side of the contact/relay, thus giving a voltage reading on both sides
maybe i should have asked first ... was he checking line to ground? ask him to try checking 240v line to line he might just find a 0 reading
Could be high impedance meter, or could be one side of the contactor is shorted allowing voltage to be read through the load. Diagrams of measuring technique would be helpful. Where are the meter probes placed?
wow, i had to read it again to see that, um maybe you should delete that post, i dont want any shocking effects on something i stated
Don't all units come with a double pole contactor? I have a boxful of old ones, and they're all double pole except one is a three pole contactor.
I think your post is on point. The "misunderstanding" I referenced is that a lot of folks don't realize that in breaking only 1 line the HVAC folks accomplish the goal at less cost.
thought you were referring to this in red as misunderstanding
as 0v = safe. I can read my own statements and think to myself ... (thats not right)
rattus : the ones i have been wiring only have one line contact, the other line is fed through
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
nope
yep
typical hvac contactor, IIRC the feed through side keeps the heaters in a compressor on.
nope
yep
typical hvac contactor, IIRC the feed through side keeps the heaters in a compressor on.
Learned something today. My new unit may be so equipped. Someone else installed it. Does have a 2P disconnect though.
nope
yep
typical hvac contactor, IIRC the feed through side keeps the heaters in a compressor on.
I learned that also when I replaced mine. What surprised me was how cheep they are, certainly not in price but in their quality. When I went to replace mine I purchased (2), the spare which I keep in the enclosure. There is nothing like having to replace one and you have a spare right there for you. Mine was a honeywell.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Honeywell is the most common type I have found. Carrier units especially.
The crimp on the terminals burned off on my 40 year old DayNight. Finally got tired of patching it and bought a new unit.
That's mine, I have a Carrier.
kwired
Electron manager
- Location
- NE Nebraska
nope
yep
typical hvac contactor, IIRC the feed through side keeps the heaters in a compressor on.
Where is the return path for the heater when the contactor is open? Heaters are always hooked to line side AFAIK.
A lot of people think you have to use a 2 pole contactor. It is a controller not a disconnect. A disconnect must open all lines for (hopefully) obvious reasons. A controller only needs to open necessary lines to stop operation of what is controlled. Single phase motor this means you only need to break one line. Three phase motor you only need to break two lines to stop the motor. Some controllers have instructions to break all lines sometimes but that is listing and labeling and not general controller requirements.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
I was talking about a heating coil in the compressor, not strip heat. I will see if I can find a schematic. The heater is for keeping oil warm in compressor in cold weather.
- Location
- Massachusetts
And just how would that work unless there was a neutral involved?
T
T.M.Haja Sahib
Guest
It would be looped ahead.
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
Manufacturers use single pole contactors because they are the cheapest contactors they can buy. In my opinion they are junk. If a HVAC guy tried to put one of those in my unit I would run him down the street.
T
T.M.Haja Sahib
Guest
I think they are more reliable because of lesser number of parts.
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