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  1. #1
    Join Date
    Jan 2001
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    model #30gtn060-520ka S#2100f04316. I am getting a code of t077 which is saturated suction temp is higher than leaving chilled water temp. pressures are 250 head presssure 60 suction 29 subcooling 20-24 superheat. i went through the checkout in manual for the exv board it seems ok. i did replace the chilled water leaving sensor as it was reading 7 degrees off. while i was there the suction temp was right around the chilled water temp. it only goes out on fault after we leave during low load conditions i guess when the suction temp sways aboce cw temp. the ll drier is ok ll valve wide open. on startup the exv frosts over alot longer than the other circuit(they all do that at first for a minute I think)the other circuit is running superheat around 5-6 which puts suction temp closer to 38-40.i checked windings for exv motor. i tried running circuit by itself, together with other circuit loaded unloaded superheat still high. with high subcooling and superheat would you suspect problem with txv. also last year a tech that no longer works here replaced a plugged drier.

  2. #2
    Join Date
    Mar 2003
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    high subcooling high superheat and low suction.
    overcharged and exv is not opening or is fouled.

  3. #3
    Join Date
    Dec 2004
    Work Primarily Downtown Chicago Loop Area
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    Have you also checked the calibration or accuracy of the transducer that is giving the board its suction saturation temp it could also be quite a bit off giving you this error. Just a thought.

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