Page 1 of 2 12 LastLast
Results 1 to 13 of 17
  1. #1
    Join Date
    Mar 2013
    Posts
    6

    LPS short cycling on Trane equipment

    Trying to clean up another contractors mess. New Trane system they installed this past winter, so this is the first summer with it, model numbers: TAM7A0C60H515BA;4TWR5061E1000BA.

    The air handler is their new style with an electronic TXV. It has a honeywell zoned system with 4 zones and a bypass damper. We originally were called in to fix some disconnected/unsealed ductwork, which we did (connected a return that never was and mastic'd some duct connections).

    Now that summer is upon us (NE Florida) we have a fun new issue. The customer was complaining that the c/u rapidly cycles on and off.

    After looking at how the zones were configured the smallest zones had (4) 8" drops being fed off of them, which automatically sent up the airflow concern. We were able to duplicate the LPS shut down by running it with just one zone calling (static pressure readings were through the roof of course). We tied the two smallest zones together (wired the dampers together to act as one, essentially eliminating a zone altogether) to test this theory. We also told the homeowner to let us know if it did happen again and if it did what zones were calling at the time. Well we heard from the homeowner today who said that is has been happening and more frequently and it wasn't biased as to how many of the zones were calling, he in fact noticed it even when all of them were.

    We have obviously tested and made sure the dampers were opening and closing, actually temperature wise the whole house is at the temperature the thermostats are asking for.

    Not being a Trane dealer, my question would be is there something with the electronic txv that can or needs to be adjusted? Am I missing something? I'm not sure what to do next at this point. I don't want to condemn the whole duct system if I'm missing something else to check out first.

    I'll provide some supplemental information that may help. The unit as far as we know has never actually frozen over as a result of any of these issues. Like I said it cools just fine. The LAT sensor shut down on the honeywell zone system is set to i believe 32ish degrees (we originally thought it may have been shutting down on the LAT sensor). With all zones calling the static is well within acceptable limits (under .5 total static).

    Thanks for any help! And sorry if this is in the wrong forum subsection....

  2. #2
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    5,821
    I would focus more on the electrical side of the problem rather than the ducts to resolve the main issue of the rapid cycling.
    There may be a terminal board issue with the indoor unit that may be worth looking into although there has been reports of this problem without the Hyperion handler.

  3. #3
    Join Date
    Sep 2002
    Posts
    11,541
    I think I would try a new LP control and add a 5 minute time-delay to the contactor coil circuit.

    For a damper zoned system I would always install an EPR valve in the suction line. Better to reduce the compressor capacity to exactly what is required than to cycle the compressor all the time.

    PHM
    -------





    Quote Originally Posted by g2nickk View Post
    Trying to clean up another contractors mess. New Trane system they installed this past winter, so this is the first summer with it, model numbers: TAM7A0C60H515BA;4TWR5061E1000BA.

    The air handler is their new style with an electronic TXV. It has a honeywell zoned system with 4 zones and a bypass damper. We originally were called in to fix some disconnected/unsealed ductwork, which we did (connected a return that never was and mastic'd some duct connections).

    Now that summer is upon us (NE Florida) we have a fun new issue. The customer was complaining that the c/u rapidly cycles on and off.

    After looking at how the zones were configured the smallest zones had (4) 8" drops being fed off of them, which automatically sent up the airflow concern. We were able to duplicate the LPS shut down by running it with just one zone calling (static pressure readings were through the roof of course). We tied the two smallest zones together (wired the dampers together to act as one, essentially eliminating a zone altogether) to test this theory. We also told the homeowner to let us know if it did happen again and if it did what zones were calling at the time. Well we heard from the homeowner today who said that is has been happening and more frequently and it wasn't biased as to how many of the zones were calling, he in fact noticed it even when all of them were.

    We have obviously tested and made sure the dampers were opening and closing, actually temperature wise the whole house is at the temperature the thermostats are asking for.

    Not being a Trane dealer, my question would be is there something with the electronic txv that can or needs to be adjusted? Am I missing something? I'm not sure what to do next at this point. I don't want to condemn the whole duct system if I'm missing something else to check out first.

    I'll provide some supplemental information that may help. The unit as far as we know has never actually frozen over as a result of any of these issues. Like I said it cools just fine. The LAT sensor shut down on the honeywell zone system is set to i believe 32ish degrees (we originally thought it may have been shutting down on the LAT sensor). With all zones calling the static is well within acceptable limits (under .5 total static).

    Thanks for any help! And sorry if this is in the wrong forum subsection....
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  4. #4
    Join Date
    Mar 2013
    Posts
    6
    But that unit actually is cycling off due to low pressure. We verified with the gauges on there that unit was running an extremely low suction pressure and tipping the LPS as a result.

  5. #5
    Join Date
    Sep 2002
    Posts
    11,541
    Yes; so the LP is wearing out / worn out and you are beating the poop out of the compressor.

    Which is why I always install an EPR valve on damper zoned systems. Anything else is generally a troublesome compromise as well as a dis-service to the customer.

    So: new LP, five minute time delay, and an EPR valve are my suggestions.

    Of course you will also want to make sure that all the operating / performance numbers for the system are correct under normal conditions with all dampers open.

    Head Pressure
    Suction Pressure
    Subcooling
    Suction Superheat
    Evap air TD
    Cond. air TD

    PHM
    --------




    Quote Originally Posted by g2nickk View Post
    But that unit actually is cycling off due to low pressure. We verified with the gauges on there that unit was running an extremely low suction pressure and tipping the LPS as a result.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. #6
    Join Date
    Sep 2002
    Posts
    11,541
    Does the TEV control the SSH properly?

    PHM
    -------





    Quote Originally Posted by g2nickk View Post
    . . . The air handler is their new style with an electronic TXV ....
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  7. #7
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    3,379
    I like PHM idea

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,764
    Quote Originally Posted by Poodle Head Mikey View Post
    Does the TEV control the SSH properly?

    PHM
    -------
    Its not a TXV. Its an EEV(Electronic Expansion valve). The manual for the air handler will have a list of test to do, to see if its the EEV, one of the sensors(coil temp sensor or vapor temp sensor), or the control board.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Sep 2002
    Posts
    11,541
    Does the EEV control the SSH properly?

    PHM
    -------




    Quote Originally Posted by beenthere View Post
    Its not a TXV. Its an EEV(Electronic Expansion valve). The manual for the air handler will have a list of test to do, to see if its the EEV, one of the sensors(coil temp sensor or vapor temp sensor), or the control board.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  10. #10
    Join Date
    Aug 2009
    Location
    Beatrice, NE
    Posts
    1,746
    Check the coil sensor for the EEV, it may not be connected or in the correct position. There are pins on the board you can use the drive the EEV open or closed to see if it moves or not. My experience has been that the EEV's work well but can be slow to react under certain conditions.

  11. #11
    I have a few questions if could answer may be able to help
    1. Does this happen on start up or while it is running?
    2. Is the line set run through a chase in the slab?
    3. If it is I'm a chase can you get a temp difference between outdoor and indoor?
    4. What color is the terminal strip on the board?

  12. #12
    Join Date
    Mar 2013
    Posts
    6
    To answer some questions.

    EEV functions correctly, ran it through its self test and all is normal. The suction pressure once you start opening up zones instantly jumps up to normal/correct operating pressures.

    1. Only after running for a while then consistently
    2. Unit hangs hor. in laundry room, so the line set runs about 15 foot through the attic, then down the side wall into a pvc chase about 20-30' to the unit.
    3 and 4. Not there to check or verify.

    We have set it up to where it works as a single zone system now. Main stat turns the system on and off all dampers open all the time. Going to give it the weekend to see if the problem persists or goes away. Should know something come monday!

  13. #13
    Join Date
    Mar 2013
    Posts
    6
    Solved. The Hyperion A/H has a YI (yellow/compressor in) and a YO (yellow/compressor out) terminal. They had the tstat and compressor wired to the YI terminal, instead of having the compressor wire leaving through YO. My understanding from Trane technical support is that wiring through the YI to YO is used for freeze proctection. Shuts the TXV down and turns the c/u off when there is a problem. Which is why it was bouncing off the LPS.

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
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event