Page 1 of 2 12 LastLast
Results 1 to 13 of 15
  1. #1
    Join Date
    Jun 2019
    Posts
    9
    Post Likes

    Trane Precend - Compressor Control Question

    Hi all,

    We have a Trane Precedent (YHC092) roof top unit that we're taking control of the compressor staging via the RTRM board thermostat terminals. We have our wires landed on the Y1 (Compressor 1) and Y2 (Compressor 2). When we send a signal to start compressor 1 it does not start. The only time a compressor starts is if we try to start compressors 1 & 2 at the same time, then compressor 2 will start. We have double checked our wiring and everything is good there. We have disconnected the Economizer Module because we have taken control of the Economizer with our controls, so i don't believe the Economizer to be interfering. Is there some internal logic that is limiting us from turning on compressor 1?

    Thanks for the help,
    qv

  2. #2
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,927
    Post Likes
    Are you sure that #1 compressor is capable of operating?
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  3. #3
    Join Date
    Jan 2010
    Posts
    19,281
    Post Likes
    Quote Originally Posted by mathieule1 View Post
    When we send a signal to start compressor 1 it does not start.
    What is your "signal" are you sending ?

  4. #4
    Join Date
    Mar 2018
    Posts
    53
    Post Likes
    I don't know Trane but some manufacturers turn part of the safeties on with the first device. If this is the case and something is switch so you are turning on Y2 instead of Y1 then that might be the cause.

    They could also use a Stat to disable Y1 when the outside temp is below a value to use the economizer to try free cooling first, then enable Y1 when Y2 is turned on because free cooling didn't work. This would happen even when the economizer is controlled in a different way. I don't know if this is the case.

  5. #5
    Join Date
    Jun 2019
    Posts
    9
    Post Likes
    Thread Starter
    Quote Originally Posted by VTP99 View Post
    What is your "signal" are you sending ?
    24v

  6. #6
    Join Date
    Jun 2019
    Posts
    9
    Post Likes
    Thread Starter
    Quote Originally Posted by Paul Benkovitz View Post
    I don't know Trane but some manufacturers turn part of the safeties on with the first device. If this is the case and something is switch so you are turning on Y2 instead of Y1 then that might be the cause.

    They could also use a Stat to disable Y1 when the outside temp is below a value to use the economizer to try free cooling first, then enable Y1 when Y2 is turned on because free cooling didn't work. This would happen even when the economizer is controlled in a different way. I don't know if this is the case.
    We tried to enable Y2 first as well and did not get the corresponding compressor to turn on.

    Interesting, i thought if you remove the ECA then the unit does not believe it has economizer capabilities and therefore does not use economizer logic. i'm not 100% on that though.

  7. #7
    Join Date
    Mar 2018
    Posts
    53
    Post Likes
    Quote Originally Posted by mathieule1 View Post
    We tried to enable Y2 first as well and did not get the corresponding compressor to turn on.

    Interesting, i thought if you remove the ECA then the unit does not believe it has economizer capabilities and therefore does not use economizer logic. i'm not 100% on that though.
    I don't know Trane so you may be correct. You could re-enable the ECA to see if that fixes it.

    I would go through the schematic to find out what else could be stopping Y1 from engaging the compressor. What you describe shouldn't be happening.

  8. #8
    Join Date
    Jan 2010
    Posts
    19,281
    Post Likes
    Quote Originally Posted by mathieule1 View Post
    24v
    So your using some type of remotely operated switching relay ?

  9. #9
    Join Date
    Dec 2018
    Location
    Texas
    Posts
    26
    Post Likes
    Did you cycle power off and back on after disconnecting the ECU? Otherwise it will still be looking for the module. The earlier years required a seperate tstat conversion board. I have had issue with the conversion board before. Are you getting 24v out of the RTRM plug? Need more info please

  10. #10
    Join Date
    Jan 2008
    Location
    New Jersey
    Posts
    138
    Post Likes
    Most units have a jumper installed when the economizer is not installed. If you removed the economizer plug and didn't install the jumper, this could effect the compressor operation.
    The wiring schematics would show this, if it applies to this rtu

    Sent from my ASUS_P00J using Tapatalk

  11. #11
    Join Date
    May 2004
    Location
    SE Pennsylvania
    Posts
    1,931
    Post Likes
    Trane does not use jumpers. It uses modbus between the controllers to determine what is installed. Does the unit have RTOM board? Is so try disconnecting that.

  12. #12
    Join Date
    Jun 2019
    Posts
    9
    Post Likes
    Thread Starter
    Quote Originally Posted by VTP99 View Post
    So your using some type of remotely operated switching relay ?
    Yes that is correct. Thank you

    Quote Originally Posted by ChillerTech3384 View Post
    Did you cycle power off and back on after disconnecting the ECU? Otherwise it will still be looking for the module. The earlier years required a seperate tstat conversion board. I have had issue with the conversion board before. Are you getting 24v out of the RTRM plug? Need more info please
    Yes, we power cycled the unit because the supply fan was able to run. The tstat conversion board, I'll have to look into that, but in any case our unit is from 2014. Yes, we are getting 24v out of the RTRM plug. Thank you

    Quote Originally Posted by chander View Post
    Most units have a jumper installed when the economizer is not installed. If you removed the economizer plug and didn't install the jumper, this could effect the compressor operation.
    The wiring schematics would show this, if it applies to this rtu
    Sent from my ASUS_P00J using Tapatalk
    We did not jumper anything out. We only unplugged the J2 plug from the RTRM. Thank you

    Quote Originally Posted by hvac69 View Post
    Trane does not use jumpers. It uses modbus between the controllers to determine what is installed. Does the unit have RTOM board? Is so try disconnecting that.
    If we unplug the RTOM board, would we lose a lot of other functionality? There are a number of different plugs going into the RTOM. Also, our client does not have BACnet capabilities (yet). Thank you

  13. #13
    Join Date
    May 2004
    Location
    SE Pennsylvania
    Posts
    1,931
    Post Likes
    There is 2 brass jumpers across the terminal block that are used to disable compressor stages. Make sure they are in place and that the wires are connected behind the terminal strip.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Contracting Business
HPAC Engineering
EC&M
CONTRACTOR