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  1. #1
    Join Date
    Jun 2008
    Posts
    35

    Mitsubishi ductless split with a short line set

    I recently installed a Mitsubishi MUH-09TW. This unit was not being used in one location and moved to another building. Prior to be moved there were no issues.

    In the new location I mounted the condensing unit on brackets and ran the lines straight out through the wall. The lineset turned out being only about 3' long. I've read the specs on this unit and it doesn't mention anything about removing charge for a short lineset (total charge 2 lb 3 oz).

    The unit's small (liquid?) line is frosting up from the king valve to a couple of coils in the evaporator. Supply air today was 71 degrees, outside temp is 82 dewpoint 72.

    It doesn't seem to be cooling properly but short of reclaiming and recharging I'm not sure which direction to go.

  2. #2
    Join Date
    Mar 2012
    Location
    New Hampshire
    Posts
    84
    Is sounds like it's metering at the king valve? Possible restriction? Low charge? If you do end up doing a recovery, I would blow the condenser out with nitrogen. I went to a call after one of our techs that only weighed in 1.5 lbs, it needed 3 (2 head unit), the tag said 1.5 lbs per head unit. The shortest lineset that I have charged was about 6' and it purred like a kitten with the factory charge. Let us know what you come up with.

  3. #3
    Join Date
    May 2010
    Location
    Oxford, UK
    Posts
    336
    Weigh in a fresh charge, but adjust it for the short pipe run, usually there is a minimum pipe run of about 10ft but check with Mitsi tech dept. Then see how it runs.

  4. #4
    Join Date
    Jun 2008
    Posts
    35
    Turned out it was a bad 4 way valve.

  5. #5
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,114
    A bad 4 way valve will not cause frosting.....

  6. #6
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,040
    Quote Originally Posted by chuckcrj View Post
    A bad 4 way valve will not cause frosting.....
    Your not suggesting the mitsu/fujitsu tech support have ever diagnosed a wrong part, are you?

    Lineset is to short.

    There is a reason that you can't buy a lineset shorter than 15'.
    "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

  7. #7
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,114
    Quote Originally Posted by hvacvegas View Post
    Your not suggesting the mitsu/fujitsu tech support have ever diagnosed a wrong part, are you?

    Lineset is to short.

    There is a reason that you can't buy a lineset shorter than 15'.
    They can only work with the info they're given. I work on them all the time, and rarely have to call tech support anymore.

    Please explain how a lineset that is too short would cause freezing?

    Fujitsu has a 9 ft minimum line length. Mitsubishi does not publish a minimum length. It is only for noise concerns that you want a minimum line length, they work just fine with a 3 ft line set.

  8. #8
    Join Date
    Jul 2012
    Location
    Southwest
    Posts
    114
    I think its a charge or restriction issue.

  9. #9
    Join Date
    Aug 2012
    Location
    Vancouver Island, British Columbia
    Posts
    16
    Quote Originally Posted by chuckcrj View Post
    Fujitsu has a 9 ft minimum line length.
    what fuji's are you working on? just curious

    The ones we install if it is a single the first has to be 16' and and if a dual head the second must be 33' with a minimum of 49' total and max of 150'

  10. #10
    Join Date
    Aug 2008
    Location
    Burlington , Mass
    Posts
    470
    Fujitsu requires 9 feet for cooling units and 16 feet for heat pumps
    I'll be there when I get there and not a minute later

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