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  1. #27
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    534
    Quote Originally Posted by cuchulain View Post
    In all reality your not suppose to pump a scroll compressor into a vacum state anyway
    they say not below 25psi, not enough oil pressure to maintain that thin film between the scrolls, and they start scraping against each other

  2. #28
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    4,661
    Quote Originally Posted by cuchulain View Post
    In all reality your not suppose to pump a scroll compressor into a vacum state anyway
    We aren't talking about pumping a scroll into a vacuum. Not in that way.

    Chuck, I know what your saying, but my only concern is with the customer. You can't tell me that needle hasn't dropped like a rock on you before. It's done it to me. On something as much of a crapfest of a happy customer as a warranty replacement coil (which btw, we are starting are rounds again....*sigh*), why take the chance? We usually just close it off, recover, repair, pump, recharge (virgin).
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  3. #29
    Join Date
    Jul 2010
    Location
    North Carolina
    Posts
    83
    TXV, he added refrigerant thinking it was low most likely but the pressures never changed. Since they didn't TXV. just let them change it a TXV is a simple device that can go bad easily.

  4. #30
    Join Date
    Jul 2005
    Posts
    5,153
    Quote Originally Posted by catmanacman View Post
    if a system is properly charged on start up and then the txv fails you have high sub cool and high superheat if he added refrigerant to get the proper sub cool then either the unit was not charged correctly on start up or the refrigerant leaked out.if the tech that replaced the txv followed proper procedures then the system should leak free
    A restriction at or within the metering device will cause a drop in SC.

  5. #31
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    Quote Originally Posted by hvacrmedic View Post
    A restriction at or within the metering device will cause a drop in SC.
    Thank you! I was gonna say the same but you beat me to it.

    Hey folks, if you ever hear anyone dissing "all that refrigeration theory crap", tell them to take a long walk off a short pier.
    • 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. #32
    Join Date
    Jul 2005
    Posts
    5,153
    Quote Originally Posted by shophound View Post
    Thank you! I was gonna say the same but you beat me to it.

    Hey folks, if you ever hear anyone dissing "all that refrigeration theory crap", tell them to take a long walk off a short pier.
    The problem is that some of the theory presented is wrong. We hear things like "SH and SC tell you where the refrigerant is in the system.". Well that's a nice thought. It is however a misguided thought. With a complete restriction at the MD all of the refrigerant gets trapped in the condenser and LL. Nevertheless the SC will stabilize at exactly 0.

  7. #33
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    Quote Originally Posted by hvacrmedic View Post
    The problem is that some of the theory presented is wrong. We hear things like "SH and SC tell you where the refrigerant is in the system.". Well that's a nice thought. It is however a misguided thought. With a complete restriction at the MD all of the refrigerant gets trapped in the condenser and LL. Nevertheless the SC will stabilize at exactly 0.
    Yes, my statement was based on the assumption that correct refrigeration theory was being taught. Regardless the point you raise is a good one. I would rather say "Superheat and subcooling tell you what is going on in the evaporator and condenser" vs. "SH and SC tell you where the refrigerant is in the system". The refrigerant is everywhere in the system! It's undergoing changes throughout the entire system! It's up to the tech to know what these changes signify, and whether such changes are normal or not.

    With a restricted metering device, there is little heat load picked up in the evaporator entering the condenser to be rejected. Head pressure falls due to lack of heat load. Pressure and temperature are relative; if the temperature via heat load is reduced, so will the pressure be reduced. And with that the saturated condensing temp approach to outdoor ambient temp (the basis for subcooling). Liquid stacks in the condenser, reducing the amount of coil that can actually condense superheated vapor from the compressor back to a liquid. If the vapor is able to condense at temperatures near outdoor ambient temp, there won't be much subcooling.
    • 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.

  8. #34
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,581
    Quote Originally Posted by curtbsa View Post
    I really appreciate all the replies. A new tech came out. Said first tech had added refrigerant to do diagnostics. He replaced HVX, emptied system and refilled. Said should be good to go. Did not give me new pressure readings though. Seems to be cooling now. I'll be back if any more problems. Thanks again.
    I would ask what the pressure where /temps and T.D. after charge. You are owner of system..Required info..
    "Everyday above ground, is a good day".
    "But everyday that you have made a difference in someones life, may insure you stay above ground a little longer".<aircooled>

  9. #35
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,978

  10. #36
    Join Date
    Jan 2010
    Location
    North Huntingdon,Pa
    Posts
    356
    Quote Originally Posted by rselby View Post
    What was the ambient temperature? He didn't calculate superheat, which would have been really nice to know. Shooting from the hip, yes you have a leak and a 7* split (with missing information) could be a TXV, but I'd need more info to be exact.
    He should have noted superheat,on a fixed txv,mfgs wants 10-11 degrees subcooling,the superheat is what it is at that designed subcooling number.
    PA#9377
    Your Satisfaction...Our Goal.

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