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  1. #1
    Join Date
    Jul 2002
    Location
    NorthEast
    Posts
    811
    a new 3 ton Mitsubishi condnesing unit

    The suction is 75 P.S.I. the room is 89 Deg.

    The unit cools the room right down to 74 Deg.
    The small 3/8 inch liquid line leaving the unit
    1) Pulsates
    2) Does not show any condensation like the suction line

    The old unit had an open compressor
    they replaced the unit one week ago
    they also installed a suction line drier


    1) Is the unit overcharged ?
    2) Should I remove the Suction line drier ?
    3) Is the pulsation normal ?

    Thank You

  2. #2
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,758

    Mitsubishis can make fools out of the best.

    I would weigh in the nameplate charge to start with, before you get too excited. It is real easy to overcharge one of these units trying to eyeball the charge. Your suction pressure tells me you don't have a shortage of refrigerant, that's for sure.

    They have their own theory of fan control as well as liquid metering. I had one recently that came from the factory with the wiring to the two HP switches reversed. Couple that with a goofy outdoor unit coil thermister, and hi head was the fault at 365# instead of 450 something like the information
    buried in the parts list said. The lower of the two switches is supposed to tell the board to give full fan speed. In normal operation, the board tries to satisfy the outdoor thermister.

    Anyone who has ever worked on one of these has scratched their head more than once. Tojo's revenge.
    God Bless the USA

  3. #3
    Join Date
    Jan 2005
    Location
    steeler nation
    Posts
    2,027
    the only way to charge a ductless split is to weigh in the charge taking into account the length of the line set. no other way to do it. pain in the ass but your wasting your
    time trying anything else.

  4. #4
    Join Date
    Mar 2004
    Location
    Janesville WI
    Posts
    419
    you have to becarful here what you think is a liquid line is not, the metering is done at the condenser, some of the older indoor wall units were not compatible with the newer condenseing units(metering)

  5. #5
    Join Date
    Jan 2005
    Location
    steeler nation
    Posts
    2,027
    mr slims have the expansion device in the condensor to reduce the noise at the evap. if you look in the condensor you will see access ports that are tucked above the compressor this is where you get condensing pressure. i think they call the liquid line "saturated liquid line".
    suction pressures are usually low in the low 60's.

  6. #6
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    whatm is your superheat and subcooling and your delta's. Cmon Man.

  7. #7
    Join Date
    May 2005
    Posts
    1

    Overchage thats a joke

    I have a split system that has been giving me problems for a while. It turns out that the outside board was bad so I replaced it. I had been getting a P-8 code. One of the things it said was a undercharge. I should of only had 5lbs. 8oz with maybe a few extra ozs. for the extra line. When I was done I removed almost 13lbs. I pulled a vaccum to check for leaks. I was able to get it down to 1,000 microns before I had to go home. On Monday if the vaccum holds I plan on charging it with the proper charge and hope it works. We have a bunch of them at the hosiptal so who knows what else is out there.

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