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I have an old central vac unit I would like to use as a dust collector, but I am hesitant about the wiring. It has a double set of low voltage wires. Black and white, and red and green.

  • Black and white go to a 120 to 24 transformer,
  • while the green and red go to a switch to turn on the higher voltage.

Any version of opposites will turn the motor on

  • Red and white
  • Green and black
  • Black and red
  • Green and white

Similar will not turn it on (black and white or green and red).

All four wires are low voltage. 30 volts max.

There is a 3 prong wall plug to supply the actual running voltage to the vac, I am just wondering about the low voltage wires, the one’s that usually run to the wall outlet and control on and off.

Any idea which two ( or even four) should be used to turn on the motor?

Not sure if it matters but it’s an airstream sf207a. Couldn’t seem to find a wiring diagram. Thanks.

Rob Tex
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  • to me your post makes no sense. black and white are 120 V to transformer. – Ruskes Dec 24 '22 at 01:25
  • `while the green and red go to a switch to turn on the higher voltage. ` what is the meaning of this ? what higher voltage ?? – Ruskes Dec 24 '22 at 01:28
  • The "higher voltage" is the 120 or 240V the motor runs off of @Ruskes – ThreePhaseEel Dec 24 '22 at 01:56
  • All four wires are low voltage. 30 volts max. I was a little unclear. There is a 3 prong wall plug to supply the actual running voltage to the vac, I am just wondering about the low voltage wires, the one’s that usually run to the wall outlet and control on and off. – Rob Tex Dec 24 '22 at 02:42

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I will take a SWAG: from what I have seen it sounds like they wired it such that a DIY could easily install it. Black and White, power. Red and Green, Switch. Now the switch needs power to turn on the relay so one of the switch leads needs to be connected to one of the power leads. The other two go to the relay coil When on the phone this makes it simple to troubleshoot and explain to the DIY what to do.

Gil
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