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Thread: Mcquay unit vfd

  1. #1

    Mcquay unit vfd

    Got a mcquay rooftop unit RPS model, problem is the vfd will not run the blower motor, the blower will only run in bypass. I don't even get a display on the vfd, I'm wondering if Its the vfd itself or if it's being locked out?

  2. #2
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    Most likely the VFD itself.

  3. #3
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    anytime the breaker is on to the blower the vfd should have a display. since your blower runs in bypass the breaker is on. verify the power at the vfd with toggle switch in vfd position.

  4. #4
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    The unit most likely has a bypass and drive contactor. Is the drive contactor closing, do you have power to the drive? Is the red fault light lit under the display, do you have 24 volts DC across terminals 10 and 12? If you do swap displays to see if the display is dead or if there is a fault in the drive.

  5. #5
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    The drive is bad, are the vfd's difficult to replace,ive seen it done working with a co worker,but not sure about setting the parameters, and everything?

  6. #6
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    should be programmed from the factory for the specific application and unit model #.

    Pretty easy to install. VFDs can be hazardous to your health so read any and all information that comes with it.

  7. #7
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    Quote Originally Posted by etheric999 View Post
    The drive is bad, are the vfd's difficult to replace,ive seen it done working with a co worker,but not sure about setting the parameters, and everything?
    If your display didn't die and if your lucky some one uploaded the config out of the drive onto the display you can attach the old display to the new drive and download the config to the new drive.

    If you have an identical unit on the roof, connect the new display upload the config then attach the display to the new drive then download the config.

    Make sure you select the proper upload to and from options or you will have two drives to setup.

  8. #8
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    Quote Originally Posted by hvac69 View Post
    If your display didn't die and if your lucky some one uploaded the config out of the drive onto the display you can attach the old display to the new drive and download the config to the new drive.

    If you have an identical unit on the roof, connect the new display upload the config then attach the display to the new drive then download the config.

    Make sure you select the proper upload to and from options or you will have two drives to setup.
    Ive replaced 3 VFDs on two different brands of RTU units. Both manufacturers sent the drives preprogramed.

    Does McQuay not. offer this option ?

    Also if he didnt the experience to condemn the drive is it a good idea to suggest he swap display modules when programming from the factory is available ?

  9. #9
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    Quote Originally Posted by commtech77 View Post
    Ive replaced 3 VFDs on two different brands of RTU units. Both manufacturers sent the drives preprogramed.

    Does McQuay not. offer this option ?

    Also if he didnt the experience to condemn the drive is it a good idea to suggest he swap display modules when programming from the factory is available ?
    Honestly a good idea would be for him to get off the roof and call someone that knows what they are doing in the first place. I was merely giving him an alternative as I have replaced dozens of these and only a few from the OEM manufacturer and have never had one come from factory configured. Also I would never trust that the drive was configured properly in the first place. Plus I try not to buy from the manufacturer as their prices are usually double of what I can get them for and usually have a 1 to 2 week lead time, why wait when I can set up from scratch.

  10. #10
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    I hear you.

    True story. After my munters unit blower VFD went thermonuclear on me I called them and had a preconfigured drive sent out.

    Their cookie cutter approach to programing the new drive cost me a call back because of an incorrect deceleration parameter....OC fault.

    In hind sight its not a bad idea to log drive confifurations and hold on to them just in case.

    Also if hes asking " if they're hard to install" then I would agree he needs to leave the replacement to someone more quallified.

    Especially if its shipped minus the program.

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