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  1. #1
    Join Date
    Jul 2005
    Posts
    4

    Hmm

    I've installled a TXV (Sporlan CBBIVE-2-GA, exterbnally equalized) in the evaporator. The system seems to provide good cooling but after the system stops, the pressure in the lines does not equalize. As a result compressor cannot start again. It starts again only after resetting the changeover valve. I had to install a piston back temporarily.

    Is there something wrong in the way the TXV works?
    Or do just I need to add start assist to the compressor?

    The compressor is hermetic Copeland CR18KQ-PFV. TXV's equalizing tube was connected correctly and wasn't capped.

    Any help is appreciated.

    Thanks.


  2. #2
    txv's have to have a start kit. also you installed a txv that does not equilize (hard shutoff)

  3. #3
    Join Date
    Jul 2005
    Posts
    4
    If I install a hard start kit, wouldn't it be potentially damaging for a compressor to start against high pressure every time?

  4. #4
    no

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,290
    Originally posted by dkrants
    If I install a hard start kit, wouldn't it be potentially damaging for a compressor to start against high pressure every time?
    Nope. A start capacitor gives the compressor the needed boost to overcome the static pressure on the piston head. There are hermetic pots out there that have had pot relays and start caps and have been humming along for years.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Join Date
    Apr 2002
    Location
    Ann Arbor, MI
    Posts
    2,985
    Originally posted by dkrants
    I've installled a TXV (Sporlan CBBIVE-2-GA, exterbnally equalized) in the evaporator. The system seems to provide good cooling but after the system stops, the pressure in the lines does not equalize.
    That is part of the reason why the TEV provides a higher SEER rating than a piston/restrictor.

    Since the pressures do not equalize, the compressor spends less time pulling suction pressures down upon start up. With a piston, the compressor must spend more time getting pressures to design conditions.

  7. #7
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    Originally posted by Andy Schoen
    Originally posted by dkrants
    I've installled a TXV (Sporlan CBBIVE-2-GA, exterbnally equalized) in the evaporator. The system seems to provide good cooling but after the system stops, the pressure in the lines does not equalize.
    That is part of the reason why the TEV provides a higher SEER rating than a piston/restrictor.
    I don't think this is true, since most new high SEER units use scrolls, which allow equalization when stopped.

    paul

  8. #8
    Join Date
    Apr 2002
    Location
    Ann Arbor, MI
    Posts
    2,985
    If system pressures equalize during off-cycle, then the unit is less efficient than one which does not allow pressures to equalize. The SEER "D" test measures system efficiency when the unit is cycled on and off.

    Scroll compressors utilizing a discharge check valve should hold differential pressure, unless the check valve leaks. The check valve, as I recall, prevented the scroll compressor from "unwinding" during off-cycle which created a loud noise. I'm not sure if current scroll compressors utilize a discharge check valve.

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