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  1. #1
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    P66 Head pressure control question.

    Trane:
    TWE120B300EA
    3294XX85H

    I am wanting info on how the P66 operates internally. Does it drop volts and raise amps, or does it have the ability to drop voltage and lower amps like a VFD? I seriously doubt the latter is the case, but I will explain at the end why I ask.
    I have 3 of these exact units on a roof. I had a P66 factory controller go bad. I replaced with a ICM 325 with 2 sensors since I have 2 Circuits to read. Started getting intermittent issues. Looking at the trend since it does a computer room it was happening at night. scheduled myself at 5am to diagnose during low ambient. Sure enough fan cycling control slows motor down, and amps double, and eventually hits thermal.

    Called Trane, and found wrong Motor. Ordered exact factory motor, and installed.

    P66 still almost doubling amps while slowing down with brand new factory everything! I walk over too the unit beside me. That units fan is running a quarter speed and dropping amps as it slows down!

    Only difference I see is one P66 is BAB-5, and the other is BAB-2. That's just pressure and should not make much difference.

    I have the factory motor in there which has a service factor, and power factor too handle the amps. I just don't get why the two units beside me drop amps while slowing down fan. I just don't see that happening in that tiny P66 box.

    It's wired exactly the same, and Voltage is exactly the same. It's a 3 wire motor, and everything attached too it is new! I'm just baffled why the two beside me drop voltage, and the one I am having issues with is raising voltage.

    any help is appreciated!

  2. #2
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    It varies the voltage.

    As volts go down, amps will go up.

    The motor needs to be ball bearing. No sleeve bearings.

    It is suggested that the motor have a heatsink for low operating speeds due to more heat being generated.

    The 24vac power supply MUST be on the same phase as the motor. Ex: (motor L1, L2 are on phase B and C. The transformer primary should also be on phases B and C)

    Also, check your coils. They are more than likely a double row coil and they have a sheet of dirt on the inside. This will also cause the motor to burn up


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  3. #3
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    that is the indoor unit model number.....outdoor would be a TWA or TTA. neither of those units show a P66 (or any) speed control in the wiring diagram, only an optional ON/OFF fan control with the indoor coil freeze stat for low ambient.

    are these controls factory installed? I wonder if they are wired wrong, as gravity said, your transformer has to be wired correctly to L1/L2. download the P66 installation and operation manual, and compare to what you've got. The -2 vs. -5 is just a pressure range....make sure that's for the correct refrigerant.

    also, the factory correct motor may not be a ball bearing motor....especially if it's for an ON/OFF ambient control.

    regarding the ICM325. Since it is temperature based, you have to play with the sensor placement, as there is a significant lag in external pipe temperature vs. internal pressure/temp. and you have to be very careful with the low speed adjustment.....be sure it's set for the correct motor type. I'm not really a fan of those, although I've used them successfully.

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  5. #4
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    Quote Originally Posted by 71CHOPS View Post
    that is the indoor unit model number.....outdoor would be a TWA or TTA. neither of those units show a P66 (or any) speed control in the wiring diagram, only an optional ON/OFF fan control with the indoor coil freeze stat for low ambient.

    are these controls factory installed? I wonder if they are wired wrong, as gravity said, your transformer has to be wired correctly to L1/L2. download the P66 installation and operation manual, and compare to what you've got. The -2 vs. -5 is just a pressure range....make sure that's for the correct refrigerant.

    also, the factory correct motor may not be a ball bearing motor....especially if it's for an ON/OFF ambient control.

    regarding the ICM325. Since it is temperature based, you have to play with the sensor placement, as there is a significant lag in external pipe temperature vs. internal pressure/temp. and you have to be very careful with the low speed adjustment.....be sure it's set for the correct motor type. I'm not really a fan of those, although I've used them successfully.
    Icm333 with a icm380(pressure transducer) is a better option than the 325


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  7. #5
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    What gravity and CHOPS said.

    Also, ....I converted a couple of Voyagers about 10 years ago, using trane BB motors and 2 pressure P66.

    They've run fine since. The amps do go up, but that is normal. If you want the amps to not rise above FLA then you have to use the P266 I believe.

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  8. #6
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    Thread Starter
    A Update on the progress. I'm kinda stupid on this one, but I learned a few things in the process so It's a good thing. The P66 is not the issue. I went over that wiring on the entire unit tooth and nail. p66 is working fine. Here is the story on this.

    I have 3 exact units side by side doing computer spaces. I am working on #2. #1 and #3 work fine. Customer had intermittent issues at night. I arrived early because I suspected low ambient. Sure enough Hitting thermal. Someone before installed a ICM325. With the issues I was having I hooked back up the P66 and it worked fine so someone had this same issue before me I assume.

    Contacted Trane and ordered the exact motor in #1 hooked to a P66 with no issues. Installed and ran 3days out on thermal again!

    Contacted Trane and they said we are extremely sorry. We gave you the wrong motor. I thought Great, let me go get the correct one!

    At Trane in MD I saw the motor. I told her that motor won't work. She assured it will, and my motor is discontinued but this is the new part# Now granted I have the OEM motor in the exact unit beside me that works fine so I assumed I would just stick with OEM. I always try to stay OEM if at all possible, Especially AAON.

    Installed new motor and at full speed pulled perfect RLA. Hooked to P66 Voltage dropped to 319V/3A when RLA is 2.4. Ran for 30 minutes before showing smoke, and getting boiling hott! At that time I was done with OEM and called Johnson Controls Development and got specs on a motor that would for sure work with this application. It's on order! Customer has cooling because we have not hit enough low ambient too warrant a emergency yet.

    I'm at fault for not putting a motor rated for the application in the first place. I assumed since the OEM motor is beside me working it would be fine. Some say the unit did not come with a P66. I agree according too online. I checked Trane 360 and there is no record of it. There is documentation inside the unit from 2003 that shows wiring from Trane for the installed P66. Possibly a custom order unit??

    Anyway, I let this unit drive me way more crazy then I should have. I take ownership of the mistakes, because I know motor ratings for speed control, and if it's not listed on the motor I should assume it does not have them! I should never assume OEM means it does!

    Just thought I would give you a update on the issue! Thanks for everyone's help! The most important thing is my ability to keep the customer happy. That truly is the most important thing! It will get fixed, just trust me!

  9. #7
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    Did you make sure transformer primary phases are the same as motor phases?

    Did you check the split coil to see how dirty it was.

    Both those issues will cause motor issues


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  10. #8
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    Thread Starter
    Quote Originally Posted by gravity View Post
    Did you make sure transformer primary phases are the same as motor phases?

    Did you check the split coil to see how dirty it was.

    Both those issues will cause motor issues


    Sent from my iPhone using Tapatalk
    Yes, I split the sandwhich coils and cleaned. I do the PM here so I did it last year, but did it again just to be sure. I also checked phase. That is the first things I checked after asking my question. Thanks for all your help guys! It is much appreciated.

    I can almost promise you the OEM motors run in #1 and #3 because the rooms are extremely oversized. They see very little run time at all. They are all most likely wrong. It just say happens I am working on the unit that runs all the time due to load.

  11. #9
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    Thread Starter
    Yet another update to my nightmare. Installed the new non OEM motor, and it didn't work. Called Trane and got in a 3 way call with parts, and tech support. After some researching they found that in 2003 Trane made some units with a Baylo kit installed and I just so happen to have 3 of them. Unfortunately the 3 that I have do not have the identifiers in the model and serial to tell anyone that I have those units. I need the motor that came with the Baylo kit. Trane is working on it now. Supposedly that motors windings are different. Trying to use Non OEM I would need slightly above 1hp, but can't do that because anything above 1hp goes to 3PH. I supposedly must use the Trane Motor. I'm not sure how true anything anymore. At this point I just want a motor that I can slow down with no issues.

  12. #10
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    One thing to keep in mind about motor selection is that no manufacturer can lie about amp draw. They can rate HP, wattage, etc. at whatever they want. But when it comes to amp draw, they legally have to be accurate. All wire and protection sizing is based on amp draw. Don’t forget, NEC has HVAC specific sections based on interior or exterior of cabinets also.

    You are likely dealing with motors that aren’t rated for the correct amp draw. You’re gonna have to turn into Sherlock Holmes if you want to solve this problem.

  13. #11
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    Get a ball bearing motor

    Put a icm333 with a icm380 transducer on and call it a day

    Send me details on this unit and i will look it up myself.


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