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  1. #1
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    Blower motor speed control

    I have a three ton Payne heat pump with 15kW heat strips (little insulation in the house). Presently, the fan drives the low speed on the blower motor. When the first stage of strip heat is called for, it drives the blower at medium speed. Clearly at this point, the blower motor is being driven on both the low and medium speed lines. Does the higher speed (medium) take precedence even though the low is being driven as well. I need high speed for the full 15 kW. If I just drive the high speed blower line will it take precedence over the two lower speeds even though they are being driven at the same time?

  2. #2
    Join Date
    Mar 2009
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    Clearly at this point, the blower motor is being driven on both the low and medium speed lines
    WRONG

    When the unit switches the motor speed it uses a relay to switch from on speed to the next. To run the motor on high speed switch the the high and mediums speeds, easy peazy, lemon squeezy.
    If I would of killed my wife when I first met her, I'd be out of jail by now!

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  3. #3
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    According to the schematic, W2 connects directly to medium speed (red) and FAN (green) connects directly to low speed (blue). There are no relays between the thermostat and the fan motor. Are there relays internal to the fan that cause the highest motor speed being called for to take precedence?
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  4. #4
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    Here's a better scan of the schematic.
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  5. #5
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    Quote Originally Posted by pwn01 View Post
    Here's a better scan of the schematic.
    I`m guessing you need to know what note #5 says.
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  6. #6
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    Note 5 states that if field installed heat strips are used, a change in motor speed may be needed.

    The schematic indicates that the taps to the motor are control wiring since they are 24vac. Three speed motor tap schematics that I have seen show the actual internal wiring of the motor which is 120vac. Evidently, the taps on the motor cannot be "cascaded," but must be individually wired or problems will occur.

    The schematic that I posted clearly shows that if the unit is on in heat mode, the thermostat will be driving the low speed tap with 24vac. If the first stage of electric heat is called for, the white wire and consequently the medium speed tap is energized with 24vac by the thermostat. At this point, both the low and medium speed control lines to the IFM are energized. If this is the case, the motor itself must have internal relays that open the lower speed taps when a higher speed tap is energized.

    This question only comes up because I need high speed on the fan if the full 15kW comes up. With 10kW or less, I would just leave it as it is and never question it because the medium speed energized by the first stage gives enough airflow. I just have some red flags with the possibility of having all three taps energized at the same time.

  7. #7
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    Quote Originally Posted by pwn01 View Post
    According to the schematic, W2 connects directly to medium speed (red) and FAN (green) connects directly to low speed (blue). There are no relays between the thermostat and the fan motor. Are there relays internal to the fan that cause the highest motor speed being called for to take precedence?
    Wouldn't it be easier to post a model number ? Looks like an ECM style motor which has a certain input sequence that a wiring diagram isn't going to tell us.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  8. #8
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    Give us the picture of the entire diagram including all of the notes and legends, please. Model # would be helpful.

  9. #9
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    I don't have the number in front of me. If I remember correctly, it is a Payne PH3ZNB. . . etc. 3 tons.

  10. #10
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    I'll scan the whole schematic when I get home and post it. It will be a while.

  11. #11
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    Please review the rules about who may give advice in the AOP forums.
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  12. #12
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    Quote Originally Posted by pwn01 View Post
    I'll scan the whole schematic when I get home and post it. It will be a while.
    Does it have a matched AHU if so get the model number off of it too.
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    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  13. #13
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    Quote Originally Posted by timebuilder View Post
    Please review the rules about who may give advice in the AOP forums.
    What are you talking about???
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

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