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  1. #1
    Join Date
    Jan 2006
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    85

    Armstrong 2-stage compressor question

    I recently installed a new Armstrong 3-ton, 2-stage 16 seer condensing unit, and matching a-coil & TXV on a furnace with a conventional motor. The first 3-weeks, the customer was very pleased with the unit-temperature hit set point on thermostat, even on the hottest days, system cycled on & off, house was comfortable. Then last week, the customer stated that the unit started running for hours without cycling on & off, and it was struggling to hit the set point during the hot part of the day, just like the old, undersized 2-ton builders unit that I replaced. Finally, the outdoor unit stopped running. I checked the board, and it was putting out a code that the low pressure switch had cut out 5-times, and locked out. I was expecting to see low pressure readings when I restarted the system, suspecting a loss of refrigerant, but the hi/low pressure readings were exactly where they should be, and the system was operating just as it should. The customer called the next morning, and reported the system froze up during the night. They let it thaw out, and ran it for the whole next day, but it then froze up again after about 10 hours of use. The symptoms seem to indicate to me that the system is running just at the first stage level, and not kicking into the second stage to run at full capacity. My question is, what should I expect to see happen when the compressor is running at full capacity? While I was there to reset the board, I observed the system running at both the first stage & second stage readout on the board. However, I observed that the hi/low pressure readings never changed, the amp draw never changed, and I didn't hear any change in the sound of the compressor when the board indicated it switched to the second stage. How can I confirm that the system is actually stepping up & running at full capacity? I would appreciate any insight from those that have worked with these units-I have only installed a couple of these units, never had a problem before, and don't really know what I should expect to see going on. Thanks
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  2. #2
    sounds more like a fan problem (airflow). I don't see any changes in pressures typically on first and second stage, just in amp draw. If its freezing, with a txv installed properly its likely air flow. I put a few dual stage condensers in on single stage fans (per customers request) and never had any issues.

  3. #3
    Join Date
    Jul 2009
    Location
    Columbia, MD
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    4,467
    Sounds like the txv is failing or blower motor is cutting off.

    Recently.....tons of txvs have been failing

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  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,637
    I would put a recorder in the air supply. Maybe they are turning the t-stat way down.
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  5. #5
    Check your control wires to the fan , thermostat, and condensor to ensure they are installed correctly

  6. #6
    If you have a two stage outdoor system with a single stage (PSC) motor inside, you are going to run into many more problems down the road than low pressure switch trips. The system will run fine, for a while, then you will encounter compressor/txv failures. Those condensers operate at roughly 70% capacity on 1st stage. This means that on a 3 ton system, you are moving roughly 360 CFM's too many. This is going to lead to excessive system superheat and poor performance. Bottom line: if you are going to keep the PSC furnace in place, jump Y1 and Y2 at the condenser.
    Also, you said that you replaced a 2 ton. What size line set is in place? What is the system superheat? Subcooling? How is the bulb for the expansion valve mounted? Is it insulated?
    If you look at the normal operating pressure chart, you will see that there is minimal change between first and second stage. The high side should increase (slightly) in second stage, and the low side should decrease (slightly) in second stage. The amp draw change is minimal as well. Typically you can hear the change when the solenoid energizes. Is this one of the Armstrong communicating units? Or does this unit have the Comfort Alert module?

  7. #7
    Join Date
    Jun 2012
    Posts
    38
    Quote Originally Posted by pghtech View Post
    However, I observed that the hi/low pressure readings never changed, the amp draw never changed, and I didn't hear any change in the sound of the compressor when the board indicated it switched to the second stage. How can I confirm that the system is actually stepping up & running at full capacity? I would appreciate any insight from those that have worked with these units-I have only installed a couple of these units, never had a problem before, and don't really know what I should expect to see going on. Thanks
    Like others have said you'll have issues with airflow if you PSC is only single stage, I don't know the Armstrong product the indoor unit may be good to go just depends on what its capable of.

    I would be concerned that you didn't see a change in amp draw or pressure switching from high to low. Scroll comp or recip?

    You might want to call your supply house but below is a general way to tell if a comp is switching low to high (copeland scroll 2 stage).

    Check the suction pressures at the service valves. Suction pressure
    should be reduced by 3- 10% when switching from low to high
    capacity.
    NOTE: The liquid pressures are very similar between low and
    high stage operation, so liquid pressure should not be used for
    troubleshooting.
    Compressor current should increase 20- 45% when switching from
    low to high stage. The compressor solenoid when energized in
    high stage, should measure 24vac.
    When the compressor is operating in low stage the 24v DC
    compressor solenoid coil is de- energized. When the compressor is
    operating in high stage, the 24v DC solenoid coil is energized. The
    solenoid plug harness that is connected to the compressor HAS an
    internal rectifier that converts the 24v AC signal to 24v DC.

  8. #8
    Join Date
    Jul 2009
    Location
    Columbia, MD
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    4,467
    Time to get creative. Wire in low and high speed relays off of y1 and y2

    Sent from my SM-N900V using Tapatalk

  9. #9
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,467
    I still suspect the txv. Ive also heard of a ball of solder block an equalizer line. When running it blocked. When shutoff the bead fell down. When energized it blocked off.

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  10. #10
    Join Date
    Dec 2002
    Location
    Arizona
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    4,423
    Quote Originally Posted by gravity View Post
    I still suspect the txv. Ive also heard of a ball of solder block an equalizer line. When running it blocked. When shutoff the bead fell down. When energized it blocked off.

    Sent from my SM-N900V using Tapatalk
    X2 If its a Copeland scroll it fits the frozen coil syndrome. It will usually show up after a few weeks of operation. Not saying your system is wired correctly, it sounds like it is not. But that's not why your coil is icing up.
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  11. #11
    Join Date
    Jan 2006
    Posts
    85
    Thanks for all your input on my dilemma. It appears that the frozen coil syndrome has struck again! We replaced the TXV and the problems all went away; hope it stays that way!... While I was involved with this issue, we were installing a Payne furnace & air because the customer was convinced that the equipment was superior to all else. Turns out my Payne coil with a factory TXV and the condensing unit are included in the troublesome group that is the subject of another lengthy thread on this site... Guess I have something to look forward to next spring : )
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  12. #12
    Join Date
    Jan 2004
    Location
    PA
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    68,759
    Quote Originally Posted by andrew.twitty View Post
    If you have a two stage outdoor system with a single stage (PSC) motor inside, you are going to run into many more problems down the road than low pressure switch trips. The system will run fine, for a while, then you will encounter compressor/txv failures.

    A 10 ton 2 stage RTU doesn't slow the blower when only 1 stage is calling. Running a residential 2 stage condense on a PSC blower won't harm a TXV, or the compressor when its in first stage.

    Those condensers operate at roughly 70% capacity on 1st stage. This means that on a 3 ton system, you are moving roughly 360 CFM's too many. This is going to lead to excessive system superheat and poor performance. Bottom line: if you are going to keep the PSC furnace in place, jump Y1 and Y2 at the condenser.
    Also, you said that you replaced a 2 ton. What size line set is in place? What is the system superheat? Subcooling? How is the bulb for the expansion valve mounted? Is it insulated?
    If you look at the normal operating pressure chart, you will see that there is minimal change between first and second stage. The high side should increase (slightly) in second stage, and the low side should decrease (slightly) in second stage. The amp draw change is minimal as well. Typically you can hear the change when the solenoid energizes. Is this one of the Armstrong communicating units? Or does this unit have the Comfort Alert module?
    A 2 stage condenser on a PSC motor not set up to slow down. Generally just doesn't dehumidify as well as 1 on a VS blower.
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