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  1. #1
    Join Date
    Jan 2020
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    Fans on compressor units running backwards, what would cause this?

    Our compressor units shut down a few weeks ago, the cause was that the fans on the compressor units were running backwards and a sensor shut them off to protect them from overheating.

    We have a company that does maintenance every month and this issue occurred about 1 week after maintenance had been at our facility. I know next to nothing about HVAC but for the following reasons, I'm wondering if the tech who came out left them running backwards,



    The tech who came out to do maintenance a week before the issue happened was not our regular guy. The new tech said we had all sorts of problems going on with our equipment. When our regular tech came out to fix the fans that were running backwards he said there were no issues. I got the sense the new guy wasn't just new to us.

    We've been having some cool weather in Southern California but the day they shut down happened to be the warmest day we had in several weeks (going off of memory), which makes me wonder if the fans had been running backwards and just couldn't continue operating on the warmer day.

    When I asked our regular tech what would be the reason for fans to abruptly start running backwards, he said he doesn't know and that he's never gotten a real reason from other HVAC employees at his company as to why it would happen, but he said he has seen it a few times. I asked an electrician I know what would cause fans to abruptly start running backwards and he said it's bizarre and he can't think of a reason. I searched online and I couldn't find anything.

    We have one company that does all maintenance and repairs on our refrigeration so either the new tech made a mistake or there is a bonafide malfunction that would cause this and surely someone must know the reason. The tech who fixed it added oil to the system and switched the wires on the fans to change polarity.

    Can someone offer an explanation on this?

  2. #2
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
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    A bad capacitor can cause a motor to spin backwards. I would think this would be more likely than it would have been for the tech to have caused it, but who knows?

    If the motor quits working soon then I'd say a bad capacitor (that might have been overlooked the first 2 times) was probably the cause.

    With this being said, you don't mention what type of equipment your facility has. If these are large units that have 3 phase fan motors, then they don't have capacitors. If this is the case then maybe it was the first guy messing around with the wiring.

    Also, no one should be "adding oil to the system". This is not a normal thing to do.
    If at First You Don't Succeed, Skydiving Is Not for You.

  3. #3
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Make and model of condenser

    single or 3 phase

    what controls the head pressure

  4. #4
    Join Date
    Jan 2010
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    Sea to Sky
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    Also do these units only have one fan or multiple fans in each unit?

    Is your area susceptible to high winds?

    Sent from my SM-G965W using Tapatalk

  5. #5
    Join Date
    Jan 2020
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    Thread Starter
    Quote Originally Posted by ammoniadog View Post
    A bad capacitor can cause a motor to spin backwards. I would think this would be more likely than it would have been for the tech to have caused it, but who knows?

    If the motor quits working soon then I'd say a bad capacitor (that might have been overlooked the first 2 times) was probably the cause.

    With this being said, you don't mention what type of equipment your facility has. If these are large units that have 3 phase fan motors, then they don't have capacitors. If this is the case then maybe it was the first guy messing around with the wiring.

    Also, no one should be "adding oil to the system". This is not a normal thing to do.
    From what you are saying, I think these units wouldn't have capacitors. If it was a capacitor then the tech should have said he replaced a bad capacitor, all he said was that he switched the wires to switch the polarity. Below is the information I pulled off the compressor units outside.

    Century Refrigeration
    Model DD54L7
    Power Supply 230/3/60
    Control Circuit 115/1/160
    Test PSIG 450 High Side 180 Low Side
    Compressor 1 80.8 RLA - 450 LRA
    Compressor 2 80.8 RLA - 450 LRA
    Fan Motor HP 1
    Fan Motor QTY 6
    Fan Motor FLA 4.6

    Three Phase Motors Protected Against Primary Single Phasing


    Quote Originally Posted by pecmsg View Post
    Make and model of condenser

    single or 3 phase

    what controls the head pressure
    See the response directly above, which is information I pulled off a sticker on the unit. It says "Three Phase Motors Protected Against Primary Single Phasing"

    I don't know what controls the head pressure. How would I find that out?

    Quote Originally Posted by BALloyd View Post
    Also do these units only have one fan or multiple fans in each unit?

    Is your area susceptible to high winds?

    Sent from my SM-G965W using Tapatalk
    The units have multiple fans and we aren't susceptible to high winds in this area, we barely get any wind.

    Now that I think about it, I wasn't told if one fan or multiple fans were spinning backwards. Is this important for finding the cause of the malfunction?

  6. #6
    Join Date
    Jan 2020
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    Thread Starter
    To add some more information, we had monthly maintenance on 11-21-19 and on 12-12-19 the units shut off. These are the notes the tech included after fixing the problem:


    Service for December 2019 cooler evaporator fans are not running on arrival found the condensing unit was off and not running so began going through all evaporator wiring and doing so found that the system was off on high pressure safety so rested the safety and turned the unit turn right on.

    Was going throw the system and found that all of the condensing fans are running backwards so turned off the system and switch the L1 and L2 wire turned the system back on and all the fans are now running properly.

    The system was running for a few minutes and then turned off again this me on oil safety so add some oil to the system and turned the unit back on all systems are
    running properly suction pressure is at 45psi and discharge is at 240psi check amp on all 3 motors and getting 4.3 amp on all three Lags all systems are running properly and cooler temperature is at 49 and dropping

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