Posted on by Information Seekers

The how and why of PSC motor speeds

This one is about PSC motor speeds and how they are wired for HVAC fan applications. This video is part of the heating and cooling series of training videos made to accompany my websites: www.graycoolingman.com and www.grayfurnaceman.com to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

22 Replies to “The how and why of PSC motor speeds”

  1. I think they are loop wired around, say 3 triangle spot for fasted speed. I taught this was about why blower resistance add motor speed to a degree and useing a speed controller. I find this fascinating. As I can't see the logic of the motor speeding up and fall of a Cliff. & stall out. LOL

  2. Both original and replacement run capacitor are same 12.5 MFD 440/370 VAC but new replaced blower motor has 7.5 MFD listed . Still good ?

  3. I'm replacing my blower motor in my Air Handler. The new motor is also a 220v but it has a white wire and the old does not. where does the white wire connect to? Thanks

  4. The motor shown in the video was actually a four-wire motor, but the diagram was a three-wire. The motor speed tab(bk, yl, bl, rd)wires were common.

  5. My issue is I’m not an HVAC tech. So I don’t have a cost effective way to get replacements.

  6. Your videos are amazing. I am considering swapping my ECM to a PSC. I want to use the multiple taps of the motor to connect to the ECM board and then have the variable speed. Those ECM motor modules are a pain, mine has failed. Genteq.

  8. Let me ask Grayfurnaceman, if I have the same wiring set up w multiple windings as your video suggests, can I just hook up to the shorter winding and thus increase my fan speed without doing anything else? Can I continue to use the same existing start capacitor!? I am not sure if I have the same multi winding motor as your video ( I pray I do and will check this evening) as we feel as though our fan doesn't blow with much force!! It would be awesome if we could speed this up this blowing harder!! Our bedroom vent "sucks" so to speak. Has so little force thus not cooling our bedroom as much….. We can switch out our entire HVAC system at this time however a simple switch like this of which winding to connect to would be awesome!

    I hope you see this Grayfurnaceman and respond! Your channel is very informative!

  9. Let me ask Grayfurnaceman, if I have the same wiring set up w multiple windings as your video suggests, can I just hook up to the shorter winding and thus increase my fan speed without doing anything else? Can I continue to use the same existing start capacitor!? I am not sure if I have the same multi winding motor as your video ( I pray I do and will check this evening) as we feel as though our fan doesn't blow with much force!! It would be awesome if we could speed this up this blowing harder!! Our bedroom vent "sucks" so to speak. Has so little force thus not cooling our bedroom as much….. We can switch out our entire HVAC system at this time however a simple switch like this of which winding to connect to would be awesome!

    I hope you see this Grayfurnaceman and respond! Your channel is very informative!

  10. Gray ! do you have any info on how a cap. works? I have a motor that is slow to start. I don't get a spark
    when terminals are shorted across cap.

  12. Best video i have seen on PSC especially with the wiring diagram. In my HVAC course they just handed out a PSC wiring diagram with only on main winding. Printing your diagram now. Thank you

  15. This way of changing speeds only works with psc or cap-start, cap-run motors -> that leave the start winding in the circuit at all times? When changing the run winding resistance we are changing the phase angle between run and start winding and hense the motor slip?? This increase or decrease of motor slip is what changes the speed???

    This may be getting too complicated, but i'm trying to understand better

  17. The common motor winding color code really does not exist, and it gets frustrating especially when each length is the same.  We all don't have a milliohm meter to measure the ohms of an inductive coil array.

  18. I have learned a lot from watching your repair videos for a long time. I don't normally ever work on HVAC but this past week I did have to fix my Sister's unit. I posted a video on my channel. Please view if you get time and let me know how I did or if I should be aware of anything I might have missed. Thanks.

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