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  1. #1
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    552

    Tili Multi-head minisplit

    I have this misapplied Tili multi head unit that has been giving me a headache.

    outdoor mod M30C-27HRDN1-M (27KBTUH heat pump)
    with 3 indoor heads, 2 are MSV11-09HRDN1-M and 1 is a MSV11-12HRDN1-M
    the unit is servicing heating and cooling for 3 separate suits in an old house that has been separated into different apartments

    its installed with the outdoor unit hanging off the wall 15' in the air, the 2 9K heads are about 2' above the outdoor unit and the 12K head is 12' below with an oil trap on the suction/discharge line, all the lines are insulated and run on the outside of the building, ODT was about 35* at time of testing

    got a no heat call yesterday, the 2 9K heads were calling for heat, but blowing only cold air, the 12K head was turned off and not being used. I had a call before for this unit, and I had found and repaired a leak, so I was already expecting it to possibly be low on charge. threw gauges on, was getting 180PSIG head pressure (R410a), discharge temp on 1 head was 135* on the other head, 65*(already a little confused). I couldn't immediately get access to the lower unit, so I decide to recover remaining charge, leak check and weigh in new charge. just as I get my equipment set-up, building owner was able to gain access to lower unit and fired it in heat. Instantly my discharge pressure went up to 450PSIG, discharge temps increased to around 130* on all 3 heads, and all units were blowing heat.

    what i think happened:
    the unit uses electronic expansion valves (located in OD unit) as the LLS for each head, the suction/discharge lines are then just connected to a common header inside the outdoor unit. I think that the lower unit being off for such a long time, got stacked full of liquid refrigerant, when it activated, it brought all the ref back to the OD unit, and then was operating fine.

    this makes sense to me, but how the heck do i fix it?!?!?

    anybody else experience things like this with other mini-splits? because i see lots of these units installed on a roof with the heads below them, seams to me that this could happen a lot, am i missing something

    Thanks

  2. #2
    Join Date
    Sep 2007
    Location
    Nashville,Tn
    Posts
    30
    i am just curious. what does it matter if the "liquid line solenoid" for the lower unit was off for a long time, when you get a call from the other 2 units they should still open up and meter?

  3. #3
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    552
    The other 2 did open and meter, but the hot gas line was still open to the lower unit (common header). So the ref was condensing in the line and head of the lower unit (at least that's what I am assuming). And because the LLS was closed, it couldn't get back to the OD unit. Thus making the other 2 units behave as if they were low on charge

  4. #4
    Join Date
    Sep 2007
    Location
    Nashville,Tn
    Posts
    30
    as the refrigerant goes thru the system to the 2-9's, and the 12 is off but the suction is on a common header would it not create a draw on the lineas the other ref is going by to pull out the refrigerant it needed? I could be way off here!

  5. #5
    Join Date
    Aug 2012
    Location
    NE wisconsin
    Posts
    404
    I don't have a lot of experience with heat pumps as they aren't very common up here in the great white north, but could the oil trap on the 12k head have trapped the refrigerant? How about lowering the outdoor unit so the oil trap isn't needed. Maybe someone with more hp experience has a better idea, like I said I don't see a lot of those and I could be way off.

  6. #6
    Join Date
    Dec 2008
    Location
    Ontario Canada
    Posts
    552
    Quote Originally Posted by philjafo View Post
    I don't have a lot of experience with heat pumps as they aren't very common up here in the great white north, but could the oil trap on the 12k head have trapped the refrigerant? How about lowering the outdoor unit so the oil trap isn't needed. Maybe someone with more hp experience has a better idea, like I said I don't see a lot of those and I could be way off.
    It's possible the trap is making it worse in heat mode, but the trap was added because it was oil-logging the head in the summer time

    Lowering it would be really nice , save me working from an extension latter each time, but its not going to happen

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