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  1. #1

    Excessively loud RTHA chiller loading and unloading.

    Hello, I have a RTHA chiller that seems to be excessively loud compared to my other RTHA chillers in the same plant. The chiller loads and unloads from one extreme to the other within 2 minutes. When loading up I get an A74 on the display, my pressures are 52 psi/160 psi, my chw temp is 52in/45out, amperage is at 243a, 234a, 231a. when it unloads I get A77, my pressures go up to 84 psi/ 145 psi, my temp is 57in/49 out, amperage is 119, 113, 109. discharge superheat is at 43 deg, my temp drop across the ref filter is only 2-3 deg. I am guessing that i am low on refrigerant, but not 100% sure. I have gotten different responses from other technician coworkers, but I wanted to get a little more feed back from the Forum before making my final diagnosis.

    Thankyou

  2. #2
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    I would call Trane.

  3. #3
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    Quote Originally Posted by matrix1004 View Post
    Hello, I have a RTHA chiller that seems to be excessively loud compared to my other RTHA chillers in the same plant. The chiller loads and unloads from one extreme to the other within 2 minutes. When loading up I get an A74 on the display, my pressures are 52 psi/160 psi, my chw temp is 52in/45out, amperage is at 243a, 234a, 231a. when it unloads I get A77, my pressures go up to 84 psi/ 145 psi, my temp is 57in/49 out, amperage is 119, 113, 109. discharge superheat is at 43 deg, my temp drop across the ref filter is only 2-3 deg. I am guessing that i am low on refrigerant, but not 100% sure. I have gotten different responses from other technician coworkers, but I wanted to get a little more feed back from the Forum before making my final diagnosis.

    Thankyou
    at your unloaded state you have an 18F evaporator approach and at your loaded state you have a 0F evaporator approach. if you were low on charge, i would not think that you would have a 0F evaporator approach. however, you are also experiencing a swinging condition, so it is possible that your pressures and temperatures have not stabilized enough to be valid. if your temperature drop across your refrigerant filter really is 2-3F, then you have a restricted refrigerant filter, but I doubt that you can accurately measure those temperatures, especially if you have a swinging system...you need some stability to diagnose these kinds of things. i have a feeling that your slide valve is sticking and the control system was not designed to understand and properly compensate for this condition. you will need to call in a professional to fully diagnose the issue. they may be able to get the system to stabilize and this would allow for a more accurate diagnosis.

    your amperage numbers do not mean much sisnce we do not know the voltage or frequency of this machine. %RLA would be more helpful. also, A74 is a 'normal' running condition and A77 is a 'High Current Limit' condition meaning that the chiller is running too many amps and is forcing the chiller to unload. in other words, you are not unloading and getting an A77 code...you are getting an A77 code and the chiller is then unloading....semantics is fun!
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  4. #4
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    Dear Matrix,
    As Jayguy said, to troubleshoot this unit on this issue you need stable operation.
    Let me try to decode your data.
    The unit starts and loads rapid. While loading you have A74 which is normal operation.
    At some point, the saturated refrigerant temperature in the evaporator is going close to evaporator limit (5-6°F?) and the unit enters evaporator limit state (A77) and starts to unload. As the control is not too fast, due to normal setting of control response, you can see 52 PSIG in evaporator before the unit starts to unload due to A77.
    When saturated refrigerant temperature in the evaporator is again above evaporator limit due to unloading, it starts to load again in A74 condition.
    I suggest to start the unit, let it load to electrically 60% and place it in HOLD position in order to have stable operation. If you have stable operation let it load to 80% and then put it in HOLD. After, at least, 15 minutes log the unit. Then you should be able to troubleshoot the unit.
    A lot of problems you may have, like faulty triacs, leaking or stuck load solenoid valve, internal load – unload issues etc.
    Regards,
    CV

  5. #5
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    Quote Originally Posted by jayguy View Post
    at your unloaded state you have an 18F evaporator approach and at your loaded state you have a 0F evaporator approach.
    I think you have that backwards.

    Quote Originally Posted by jayguy View Post
    A77 is a 'High Current Limit' condition meaning that the chiller is running too many amps
    A77 is evaporator limit. A75 is current limit.

  6. #6
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    80% adjustment of machine capacity and measure the evaporator aproach

  7. #7
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    Quote Originally Posted by matrix1004 View Post
    When loading up I get an A74 on the display, my pressures are 52 psi/160 psi, my chw temp is 52in/45out, amperage is at 243a, 234a, 231a. when it unloads I get A77, my pressures go up to 84 psi/ 145 psi, my temp is 57in/49 out, amperage is 119, 113, 109.
    Are you sure you are taking accurate measurements here? Why is your delta T higher when the chiller is unloaded?

  8. #8
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    It totally agree w CV , if u go to service settings( I believe )and press hold for load and unload , and pay attention to the pressure and amp draw ,. This is a good indicator if there is a problem w the slide valve leaking .

  9. #9
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    Quote Originally Posted by R123 View Post
    I think you have that backwards.
    I got a little ahead of myself there. i said loaded because he said loaded (even though he was really unloaded) which i discuss later in my post when i corrected him (but then i didn't correct myself!!)

    Quote Originally Posted by R123 View Post
    A77 is evaporator limit. A75 is current limit.
    for this one....total brain fart. i saw the current listed and didn't think things through...great catch!
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  10. #10
    Thankyou very much guys for all the responses and help with this matter. I will definetly attempt "ALL" suggestions given here once I get a chance to return to the site. However, I was told by Trane mechanics that most likely it is a bad compressor that needs to be overhauled, but before I jump to that final conclusion I will try all the other technical advice given here in the forum. I will keep you all updated on what I find asap.

    thanks

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