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I have this NEW heat recovery unit from Amazon (shady quality, branded as made in UK but actually made in China) with this motor inside. It was supposed to have two speeds (Low/Hi).

Question:
How to connect the wires?
Assuming that BROWN and BLUE and the "main" 230V wires, where do I connect the BLACK and WHITE?


Here is what I got by disassembling the unit. (Yes, the schematic I show is correct. I double checked.) Did they connected the capacitor to the wrong wire?
three wire motor diagram HRU100


Here is the user manual, which makes no sense:

HRU100 user manual PDF


Internal resistance measurement:

  • Blue-Black = 500ohm
  • Red-Black = 680ohm
  • Blue-Red = 1200ohm
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  • \$\begingroup\$ Is it a 3 phase motor? Did it work before? \$\endgroup\$ – Solar Mike Jan 13 at 15:36
  • \$\begingroup\$ @SolarMike - the unit is NEW. The user manual says it is designed for "normal" (single phase) power grid (220V/230V). \$\endgroup\$ – Rigel Jan 13 at 15:55
  • \$\begingroup\$ Does it fail? Did you ever wire it with light and switch to Hi? \$\endgroup\$ – Sunnyskyguy EE75 Jan 13 at 16:41
  • \$\begingroup\$ @SunnyskyguyEE75 - that is my point! which color is "High" (at the motor)??? Are the black and white wires high and low? In this case, if the black wire is the Hi, then the motor spins terribly slow! \$\endgroup\$ – Rigel Jan 13 at 17:09
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    \$\begingroup\$ White is high with the 1uF cap and 0.1uF is slow which agrees with your schema and their block diagram except for hi lo reversed \$\endgroup\$ – Sunnyskyguy EE75 Jan 13 at 17:39
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The hand-drawn diagram in your question shows blue and red reversed. It is possible that is an acceptable means of reversing the rotation of the motor. However it is also possible that the motor was manufactured with wire colors that do not match the manual. The resistance readings tend to indicate that interchanging the blue and red to reverse in not acceptable, but it might work even if it is not recommended by the manufacturer.

If the heat recovery unit is a manufactured item that you believe to have been installed and working properly previously, you should probably assume that the internal capacitor connection is correct. Connect the HI LO switch to white and black, respectively. Connect neutral to brown. Connect the switch and blue to power to run.

Testing:

If at all possible, measure the current when you first turn it on and compare with the rated current. Also check direction of rotation. That will prove if blue and red are properly selected assuming the product is viable at all. Resistance values indicate black/brown/5 must be hot or neutral and red, blue, 2, 3, 4 must be connected to the opposite side of the line.

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  • \$\begingroup\$ many many thanks. considering the atrocities present in the "user manual" I would not doubt that the capacitor is connected to the wrong wire!!!!!!!!!!!!!!!!!!!!!!! (PS: as you can see the manual was translated with Google Translate probably from Chinese). \$\endgroup\$ – Rigel Jan 13 at 17:25
  • \$\begingroup\$ the unit is NEW. I just didn't had the courage to installing for the last 2 years, considering the mistakes in the manual. \$\endgroup\$ – Rigel Jan 13 at 17:27
  • \$\begingroup\$ PS: why "brown to ground"? from what I know, brown is always the "live" wire. quora.com/… \$\endgroup\$ – Rigel Jan 13 at 17:34
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    \$\begingroup\$ Connecting only brown and blue connects only the presumed main winding to power. Without the aux winding, the motor can not develop much torque and could start in either direction. Your results are what I would expect and probably don't prove much. The thermal cutoff should be inside the motor. It may be covered by motor windings. \$\endgroup\$ – Charles Cowie Jan 13 at 18:43
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    \$\begingroup\$ Note that Sunnyskyguy EE75 has discovered that the hand sketch has HI and LO reversed in terms of position. The higher value capacitor will provide the higher speed. I corrected my answer. \$\endgroup\$ – Charles Cowie Jan 13 at 18:57
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So what i would try is (colors based on block colors NOT WIRE)

  • Hi->black
  • lo->White
  • Neutral->Brown
  • EARTH ->yellow/Green
  • For the last wire you need to split the hot before the switch so an always hot wire is going to blue (always meaning when you want it to run)
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  • \$\begingroup\$ And assuming that brown and blue and the "main" 230V wires, where do I connect the Hi and Low? To the ground???? \$\endgroup\$ – Rigel Jan 13 at 17:17
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Your blue is a common, red is control, and the black and brown are your supply connections. I'd say if it's a two speed motor the brown is for normal and the black is for high speed

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