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  1. #1
    Join Date
    Mar 2004
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    midwest
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    961

    Trane 60 ton low ambient problems

    Have a Raucc60 Trane condensing unit on process chiller application. In low temperatures we are over condensing causing reset relays to trip out. Unit has all stock low ambient controls, jumped out controls to monitor and found during start up of a circuit pressures drop radically before adjusting thus causing the reset relays to trip, which is normal. However, has anyone retro fitted the low ambient controls on one of these? I was thinking of a penn head pressure fan controller instead?
    An astronaut stuck in space was asked by a reporter, "How do you feel?"
    "How would you feel," the astronaut replied, "if you were stuck here, on top of 20,000 parts each one supplied by the lowest bidder?"

    "do it right or do it twice"

  2. #2
    Join Date
    Aug 2000
    Location
    USA
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    4,995
    Does this have a UCP1/695? I have made my own low ambient setups for these units. The factory controls will trip on startup every morning. I put a set of the fans on ambient control, a set on pressure control, and another set on dampers with a time delay before they start, I also added LPTDBP on the circuits. It went from a service call every morning to none when I was done with the job. The customer was tickled pink because this was an ongoing 4 year headache.

  3. #3
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    498
    I have a customer that has two 50 ton and one 60 ton Trane condensing units and one 50 ton package chiller which is basically the same unit. The chiller and one of the older 50 ton units have Penn Fan cycling controls in place of the factory low ambient controls. I was told by the tech that use to take care of the place that he was having the same problems you are having and Trane suggested installing the Penn controls. The 60 ton unit is also doing the same thing and I wanted to install Penn Fan Cycling Controls on this unit but the customer doesn’t want to spend the money right now. He is resetting it all of the time himself. All of the units have had a lot of problems like many leaks in the coils, fan motors and control problems. On the newest one, I was having a lot of high pressure problems and found that the condenser fan control wires were terminated on the wring terminals. Ckt #1 was wired to ckt #2 terminals and ckt #2 was wired to ckt #1 terminals. This is why they don’t want to spend any more money and they don’t want any more Trane equipment. I would install the Penn controls on your unit if you get the okay.

  4. #4
    Join Date
    Mar 2004
    Location
    midwest
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    961
    Thanks for advice! We were using the time delay relays on the older unit, it help out some but from time to time it would lock out. It sure made a big difference. You would think some brainless design engineer at Trane would test unit operation before they claim it works...I am seeing this alot lately Thanks again I will push for the penn control.,
    An astronaut stuck in space was asked by a reporter, "How do you feel?"
    "How would you feel," the astronaut replied, "if you were stuck here, on top of 20,000 parts each one supplied by the lowest bidder?"

    "do it right or do it twice"

  5. #5
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,532
    have you thought about hot gas bypass? of course this will be more difficult to install and test (and it can come with its own set of problems). the major benefit of hot gas bypass is at very low ambients and start up. with such a cold condensor you can still get those low suction trips on start up until the load comes up or the condensor gets warm. with the hot gas bypass you can limit those issues.

    the trane stuff works pretty good if the load is there when the oat drops. the low ambient dampers work a lot better than the low pressure switches, but you can still have the cold condensor start up issues.
    "If you pull one more stunt like you just pulled with Tommy, you won't have to get on a plane because I will personally kick your ass from here to Korea!" - Best of the Best

  6. #6
    Join Date
    Nov 2004
    Location
    North Florida/South Georgia
    Posts
    997

    In my humble opinion

    I would avoid HGBP & would also be careful about anything too radical with fan cycling controls.
    The biggest reason for this is efficiency.
    I've seen cases where someone installed FCCs & set them to keep head pressure around 300 psi.
    I would try to maintain a saturated condensing refrigerant temperature around 80* on the low end & 115* on the high end.
    Any higher & your KW goes thru the roof.
    I would try to avoid HGBP at all costs, as we all know, false loading is very costly.

    I would prefer to see you approach this from the angle that absrbrtek presented involving the bypass timer for the low pressure control.
    BUT! If you have more than one compressor in a circuit, you have to come up with a way to bypass the control for 2 to 3 minutes when the second compressor starts & the third, if there is a third.
    This could involve several additional relays, its a pain, it can be done, I've done it but it is a pain.
    When you have more than one compressor in a circuit, a good alternative to the bypass timer/timers is a manual reset low pressure control.
    It has a delay just like the oil failure controls.
    Anytime the control opens, regaurdless of if its on start up, when the second or third compressor fires or just a dip in the pressures, the heater (timer) starts to do its thing & the control has to stay open for a solid 1 to 2 minutes (depending on the specified delay) before it will lock the circuit out.
    All my leon freaked out!

  7. #7
    Join Date
    Dec 2005
    Posts
    1,923
    I thought these unit should have low pressure bypass built in it. The time lenght is depending on the outside temperature and off time.

    I would check for the condensing saturated sensor (if applicable). make sure it has good contact (use heat paste if needed).

    I always prefer VFD over any given fan pressure switch control.

    Yes it is costly but worth every penny.

  8. #8
    Join Date
    Mar 2004
    Location
    midwest
    Posts
    961
    Got 2 circuits with 15 tons scrolls in each. When that 3rd stage of cooling kicks in it drops the load pretty fast and by the time my suction pressure rises it trips. The delay relays and head pressure controls are the way to go on this one. Again, Trane should test its equipment better...You call them and its like try this and try that...give me a break!
    An astronaut stuck in space was asked by a reporter, "How do you feel?"
    "How would you feel," the astronaut replied, "if you were stuck here, on top of 20,000 parts each one supplied by the lowest bidder?"

    "do it right or do it twice"

  9. #9
    Join Date
    Apr 2005
    Posts
    517
    Quote Originally Posted by hvacdoctor View Post
    Got 2 circuits with 15 tons scrolls in each. When that 3rd stage of cooling kicks in it drops the load pretty fast and by the time my suction pressure rises it trips. The delay relays and head pressure controls are the way to go on this one. Again, Trane should test its equipment better...You call them and its like try this and try that...give me a break!
    You need to give more information. What is the full model number? What is the process temp and how is it controlled? Is the RAUCC condensing unit a low ambient with the discharge damper? What are the out door temps of operation? Not all RAUCC units are the same. What is over condensing? Is it tripping on low or high pressure?

  10. #10
    Join Date
    Apr 2005
    Posts
    517
    Quote Originally Posted by hvacdoctor View Post
    Got 2 circuits with 15 tons scrolls in each. When that 3rd stage of cooling kicks in it drops the load pretty fast and by the time my suction pressure rises it trips. The delay relays and head pressure controls are the way to go on this one. Again, Trane should test its equipment better...You call them and its like try this and try that...give me a break!
    You need to give more information. What is the full model number? What is the process temp and how is it controlled? Is the RAUCC condensing unit a low ambient with the discharge damper? What are the out door temps of operation? Not all RAUCC units are the same. What is over condensing? Is it tripping on low or high pressure?

  11. #11
    Join Date
    Apr 2005
    Posts
    517
    Suction pressure rises with a third compressor???? Dont you think the suction would drop with the addition of compressors?

  12. #12
    Join Date
    Dec 2006
    Location
    Massachusetts
    Posts
    29
    i have done many penn 66 upgrades on these units. works great.

  13. #13
    Join Date
    Mar 2004
    Location
    midwest
    Posts
    961
    Trane model # is a mile long. Its a bare bones basic set up with low ambient dampers. Pressure drops on 3rd stage start up and takes longer to adjust higher above the low pressure trip point. Sorry for leaving out the details but I try to keep the posts as general as possible. The bottom line is I have a low temp water application at 40-42 water temp to a holding tank. On demand the chiller stages as needed to keep tank water temp and also leaving and return water temperatures on the evaporators. Load is not really high so on a stage call the evap pressure drops and before it adjusts the low limit pressure control (reset) trips. I have seen suction pressure drop into the 40's before rising. The tank temperature stages 2 60-ton chillers and each chiller loads and unloads as needed. I have already spaced out the staging times to extend run periods before staging up. Again this only happens on border line load calls not every day.
    An astronaut stuck in space was asked by a reporter, "How do you feel?"
    "How would you feel," the astronaut replied, "if you were stuck here, on top of 20,000 parts each one supplied by the lowest bidder?"

    "do it right or do it twice"

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