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  1. #1
    Join Date
    Jun 2010
    Posts
    4

    Question Carrier 24ACB7 2-Stage Operation Question

    I recently had a Carrier "Comfort" Series 24ACB7 condenser installed with a performance 'N' coil (CNPVP), performance Boost 80 Gas Furnace, and a Honeywell VisionPro TH8000 thermostat (TH8321U). The air conditioner is a 5 ton unit with a 2 stage Copeland scroll (16 SEER).
    I would like to know how you can tell if the outside conedenser is switching between the first and second stage of compression. Can you hear a relay switch or can you hear the compressor motor pull more load? The outside unit doesn't seem to make more or less noise when running on the first stage vs. the second.
    The inside fan switches between a low and high speed which is very noticable and you can hear the thermostat 'click' when it sends a signal to turn on the second stage and increase the internal fan speed.
    Thanks!

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    See if the outdoor fan is spinning faster.
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  3. #3
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    Would it be nice if your thermostat told you indoor and outdoor temp, indoor humidity, equipment staging and allowed you to control fan speed?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  4. #4
    Join Date
    Jun 2010
    Posts
    4
    No, the condenser fan speed does not change; the 24ACB7 appears to have a single speed fan motor (?). I am not sure about that though... The wiring diagrams don't seem to distinguish a seperate signal to the fan motor either.
    The documentation with the unit describe the compressor operation only. It does state the compressor motor is a single speed motor-the opening and closing of the by-pass port is controlled by an internal electrically operated solenoid to go from full capacity to approximately 67% capacity.

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,043
    Does appear to be a single speed 800 RPM PSC fan motor.

    So may just have to listen for change in indoor blower and airflow.

    Or get a stat that tells you!

  6. #6
    Join Date
    Jun 2010
    Posts
    4
    The contractor that initially installed this unit did so incorrectly. They did not correctly wire the thermostat (e.g., the y2 was not correctly wired to the furnace/air handler). This issue has been corrected and the indoor fan definately changes speeds (e.g., two speeds; low and high), and the thermostat is sending signals okay. I just want to confirm the external compressor is operating correctly.
    The homeowner noticed a problem by comparing electricity usage. There was no significant reduction from the previous years usage when an 'old' 11 SEER unit was working properly. The new Carrier unit is rated 16 SEER (complete system) and should save 20-30% compared to the 11 SEER Lennox.
    I think the only correct way to confirm the first and second stages are engaging correctly is to verify the system charge by measuring the sub-cooling for high and low stage and comparing with the published sub-cool on the rating plate.
    I was currious if anyone else had experience with Carrier 2 stage units with a single speed condenser fan and noticed a noise difference or a change in the compressor load when the second stage was engaged.
    Thanks,

  7. #7
    Kuhlag

    Are you happy with the Carrier unit you bought? I'm thinking of buying the exact same unit with the Carrier VS air handler and their Edge thermostat?

    But i believe the one i was quote is a 17 Seer unit.

    Has your single speed compressor issue been solved?
    Has your electric bill gone done. Is the unit everything you expected?
    good - ?
    Bad - ?

    Any advice would be greatly appreciated.
    I know this doesn't help with your issue, but it certainly would help me out
    thanks

  8. #8
    Join Date
    Jul 2010
    Location
    DFW -> Texas
    Posts
    446
    Quote Originally Posted by restaman18 View Post
    Kuhlag

    Are you happy with the Carrier unit you bought? I'm thinking of buying the exact same unit with the Carrier VS air handler and their Edge thermostat?

    But i believe the one i was quote is a 17 Seer unit.

    Has your single speed compressor issue been solved?
    Has your electric bill gone done. Is the unit everything you expected?
    good - ?
    Bad - ?

    Any advice would be greatly appreciated.
    I know this doesn't help with your issue, but it certainly would help me out
    thanks
    I have never been sold on those 2 stage bypass units.

    For the price I think you would be better stepping up to a true 2 stage system. Pay back would be much better. When doing my payback comparisons of a 2 stage bypass and a true 2 stage system its only like a few years difference before you get your money back for the cost difference. This assumes you have received a decent price on the true 2 stage system. Some guys charge a real premium for them.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,875
    Guessing you mean the Copeland scroll compressor.

    Its still a "True" 2 stage system.
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  10. #10
    Join Date
    Jul 2010
    Location
    DFW -> Texas
    Posts
    446
    Quote Originally Posted by beenthere View Post
    Guessing you mean the Copeland scroll compressor.

    Its still a "True" 2 stage system.
    If it bypass instead of using 2 compressors or 2 speed motor in compressor its not a true 2 stage system.

    A bypass still runs the full motor with less load.

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,875
    Quote Originally Posted by Joker View Post
    If it bypass instead of using 2 compressors or 2 speed motor in compressor its not a true 2 stage system.

    A bypass still runs the full motor with less load.
    Which in turn uses far less electric then at full capacity. So it is a "True" 2 stage.

    2 compressor set ups don't use less electric then a "bypass" 2 stage.

    What is the BTU per watt rating of one of your 2 compressor systems in first stage.

    A bypass system won't use anymore electric per watt. other then if its a lower efficiency unit to begin with. EG: Comparing a 15 SEER to a 20 SEER.

    But most 18 SEER 2 stage(Copeland scroll "bypass")systems won't use anymore electric per BTU then a Trane 20i.

    In fact, they will use less electric switching back and forth from first and second stage. Then a 2 compressor system will.
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  12. #12
    Join Date
    Jun 2010
    Posts
    4
    Restaman18: In response to the questions re. the Carrier unit: the condenser is rated as 17 SEER. However, when you match it with the evaporator and furnace, it is 16 SEER. This whole system qualified for the federal tax rebate. Surprisingly, there where not that many 5 ton systems that qualified for the federal tax rebate program.
    The 2 stage compressor is driven by a single speed motor (and the condenser fan is driven by a single speed motor). The issue I have is determining if the solenoid is opening/closing the compressor bypass for one or two stage compression. I think it is working properly, but have not been able to confirm. When I get time, I am going to try to measure the amps and compare between 1 and 2 stage operation.
    My last electric bill was approx. 100-200 kWh below last year's. So, it is going down. However, the thermostat was not correctly hooked up during the entire time of the reporting cycle and it is hard to compare. So, the jury is still out on how the higher SEER relates to lower electric bills.
    My main complaints pertain to the installation of the unit as described in my earlier posts. However, the condenser unit is not as quiet as I would like it to be, but it is not excessive either. This Carrier condenser unit has no sound proofing around the compressor or on the inside of the condenser unit.
    Inside, the unit is very quiet on 'low speed'. In the afternoon, the unit will engage the 'low' speed air handler and quitly cool and dehumidify the house. I also like the Honeywell touch screen thermostat - easy to use and functional.
    Hope that helps...

  13. #13
    Join Date
    Oct 2010
    Location
    Dallas/Fort Worth Texas
    Posts
    25
    Beenthere, On a Carrier 5 ton AC system, non heat pump, that has either a two stage reciprocating or scroll compressor, can you set the point at which the second compressor kicks in? Is it something you can set on the thermostat? I called Carrier and they were worthless for help. It's like they don't know their own product. thanks

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