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  1. #1
    Join Date
    Jun 2013
    Location
    Central Florida
    Posts
    512

    Microchannel coil problems?


    Installation:

    New JROTC building at high school; York 480v, 3-phase condensing units with microchannel coils.

    Situations:

    Mechanic 'R', assigned to this school has had problems with insufficient cooling in one area in this new building.

    When I assisted him in troubleshooting the system we were unable to get proper subcooling (hot liquid line).

    Attempting to minimally increase the refrigerant charge only succeeded in spiking the head pressure and tripping the HPS.

    We recovered the charge and recharged by weight compensating by the length of the lineset according to York charging instructions.

    Again, insufficient subcooling; postulating that there might be a problem with the TXV, we ordered a replacement from RE Michel, as the unit was out of the 1st year warranty.

    When we picked up the new valve it was marked, unlike the valve in the AH, with the tonnage of the valve and did not match the size of the AH.

    Back at the school, investigation uncovered that the contractor had installed a 3-ton valve on a 5-ton AH and a 5-ton valve on a 3-ton AH.

    After correcting this f**kup, the old 3-ton valve wouldn't modulate and we wound up installing the new valve after all (in the correct unit). Problems abated.

    Things went swimmingly for the remainder of the school year, but the 3-ton began suffering from insufficient cooling a couple of weeks before school ended; now mechanic 'R' is having problems again related to or corresponding with subcooling (hot liquid line) and mechanic 'C' thinks there is a problem related to the microchannel coil.

    I have been doing some online research and have found anecdotes of problems related to York microchannel coils in particular and microchanel coils in general due to the minuscule internal passages of this design.

    It is alleged that they are seriously susceptible to blockage due to brazing scale and numerous other installation and service practices.

    In conversing with 'R' this A.M., he related that he had a problem with a York RTU at the same school earlier this week; one circuit locked out on head pressure. Long story short; HP over 500; after resetting the unit and holding the contactor in manually to bypass the thermostat time delay, thus defeating the HPS, the HP spike ended abruptly and pressures went back to normal.

    I am currently postulating that, since the factory probably flows nitrogen during assembly and brazing, this plausibly eliminates brazing scale as a possible factor?

    I am tending to reflect on the possibility of 'oil logging'?

    'R' and I are going to experiment on the split system this coming week, first week of school permitting.

    Any input of your experiences is much appreciated.
    JUST A LITTLE CLOSER AND THE LITTER BOX IS ALL MINE!

  2. #2
    Join Date
    Dec 2005
    Posts
    1,913
    Oil logged is your problem.

    To minimize oil logged problem: Crankcase heater; Or Crankcase heater and TXV; Or Crankcase heater and TXV and if possible liquid line solenoid valve.

  3. #3
    Join Date
    Jun 2013
    Location
    Central Florida
    Posts
    512
    Quote Originally Posted by just_opinion View Post
    Oil logged is your problem.

    To minimize oil logged problem: Crankcase heater; Or Crankcase heater and TXV; Or Crankcase heater and TXV and if possible liquid line solenoid valve.
    Okay. I've done some searching on microchannel coils and came across a case on the York site about an incident caused by low airflow and the hard shutoff TXVs that York uses.

    Since the original problems were caused by a TXV installation screwup I'm wondering about the advisability of going to non-hard shutoff TXV on this unit as an experiment.

    I'm also perturbed by the fact that the unit apparently cooled properly for the remainder of the school year after the initial correction?

    I don't recall if the unit had a CCH, but I know it didn't have a LLS; the lineset was only about 15' from the CU to the AHU in the mechanical room.

    There's about 2 dozen other new York units on campus and, so far, only these two have exhibited these problems.
    JUST A LITTLE CLOSER AND THE LITTER BOX IS ALL MINE!

  4. #4
    Join Date
    Jun 2002
    Location
    south jersey
    Posts
    1,102
    I'm still trying to figure out what postulating means. lol. Sounds like oil to me. Probably worked fine until the buildup of oil was too much. Not only check for cch but also check that they are functioning. With a hard shutoff txv lls is not a bad idea but I am not sure it will take care of your oil problems. Keep us informed this could get interesting. Although the factory probably purged during brazing does not mean the installing contractor did. Sounds to me when holding the contactor in he unclogged something. Oil or debris. By the way you avatar is awesome. What kind of assault rifle is kitty using?
    You need to put the phone down and get back to work!

  5. #5
    Join Date
    Jun 2013
    Location
    Central Florida
    Posts
    512
    Quote Originally Posted by jnsrose View Post
    I'm still trying to figure out what postulating means. lol. Sounds like oil to me. Probably worked fine until the buildup of oil was too much. Not only check for cch but also check that they are functioning. With a hard shutoff txv lls is not a bad idea but I am not sure it will take care of your oil problems. Keep us informed this could get interesting. Although the factory probably purged during brazing does not mean the installing contractor did. Sounds to me when holding the contactor in he unclogged something. Oil or debris. By the way you avatar is awesome. What kind of assault rifle is kitty using?
    Hypothesizingor theorizing.


    Yeah,my first approach is going to be centered on the oil. We're going toadd some Supco 88 to lower the viscosity and give that some time tocirculate through the system.

    I'vethought about the install on the split; the contractor who did itroutinely makes remarkable screwups. Probably didn't flow nitrogen.And they keep giving this shmuck contracts.

    Betyou've never seen charcoal braised TXVs. I've got to locate thosephotos for the WOS.

    Probablycan't blame the RTU on them.

    Notsure, maybe a KAT-47. Probably built it from a KIT.
    JUST A LITTLE CLOSER AND THE LITTER BOX IS ALL MINE!

  6. #6
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,031
    You like that supco 88 ! Not sure diluting the POE oil is a good idea IMHO. maybe I give the engineers too much credit but I figured the viscosity was predetermined correctly.

    Would you expand how a hard shut off valve was causing problems?

  7. #7
    Join Date
    Jun 2013
    Location
    Central Florida
    Posts
    512
    Quote Originally Posted by SBKold View Post
    You like that supco 88 ! Not sure diluting the POE oil is a good idea IMHO. maybe I give the engineers too much credit but I figured the viscosity was predetermined correctly.

    Would you expand how a hard shut off valve was causing problems?
    Well, I'm sure the HFC refrigerant people are satisfied with the overall viscosity compatibility of HFC with POE, but that doesn't mean an equipment engineer can't figure out how to screw it up with a poor design.
    I've read a number of items online about microchannel coil deficiencies and problems; mostly Yorks.
    As for diluting the oil, R421A contains a hydrocarbon based oil additive to accomplish the same thing with the existing mineral oil in R22 retrofitted systems to assist MO lubricant circulation without adding POE to the system.
    Yeah, after 38 years, I'm a Supco fan.
    I read about the hard shutoff TXV on a York website. The TXV wasn't the root cause of the investigated problem, but low air flow due to a restricted duct caused the TXV to shut down which apparently had the same effect as trying to pump down the microchannel coil. The coil couldn't hold the entire refrigerant charge and caused high head pressure which locked out the unit.
    JUST A LITTLE CLOSER AND THE LITTER BOX IS ALL MINE!

  8. #8
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,705
    Winner winner chicken dinner I think you are saying you need a bleed port TXV.


    Quote Originally Posted by EMETH View Post
    Well, I'm sure the HFC refrigerant people are satisfied with the overall viscosity compatibility of HFC with POE, but that doesn't mean an equipment engineer can't figure out how to screw it up with a poor design.
    I've read a number of items online about microchannel coil deficiencies and problems; mostly Yorks.
    As for diluting the oil, R421A contains a hydrocarbon based oil additive to accomplish the same thing with the existing mineral oil in R22 retrofitted systems to assist MO lubricant circulation without adding POE to the system.
    Yeah, after 38 years, I'm a Supco fan.
    I read about the hard shutoff TXV on a York website. The TXV wasn't the root cause of the investigated problem, but low air flow due to a restricted duct caused the TXV to shut down which apparently had the same effect as trying to pump down the microchannel coil. The coil couldn't hold the entire refrigerant charge and caused high head pressure which locked out the unit.

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