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  1. #1
    Join Date
    Mar 2005
    Posts
    657
    I put in a new condensing unit back in 2003. The customer called and said that it is making noises when it starts up. I went and listened and it makes a kind of a knock when it starts up. It runs quiet and fine after the first couple of seconds. I don't think it has a expansion valve. Someone else installed the furnace and coil. I am sure that they are matched as to size.
    Anyway the condensing unit is on the ground and the evaporator is in the attic about 10' higher than the condensing unit. I came horizontal out of the condensing unit about 2' horizontal, then straight up about 10' then went horizontal ( and maybe slightly up hill) about 8' to the evaporator.
    Could this cause the compressor to slug. I called the distributor that I got this from, and they said you need S-traps on 20' of rise. However they thought it might be a good idea to put one this system.
    I also looked at a book from a copeland seminar I atended several years ago. It said that on 3' to 4' of vertical rise to put a P-trap by the condenser unit. Do any you do this. Any thoughts?
    I am going to go back and make sure as to whether it has an expansion valve or not. It is in the attic and will go when it is not so hot.

  2. #2
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,181
    This is an assumption based upon similar symptoms...

    You have liquid sitting in the compressor on start. The slight knocking noise is the liquid being moved through the discharge. If it's a scroll, it sounds a little like someone who can't shift gears real well.

    Check your charge closely. I usually find that these symptoms will disappear after removing just a few ounces of refrigerant.

    Again, this is only an assumption...need numbers to see what's really happening.

    [Edited by jrbenny on 07-27-2005 at 05:07 PM]

  3. #3
    Join Date
    Aug 2004
    Location
    Boston, MA
    Posts
    110
    If condensor is placed where it could be a cooler temp than the evap(evap in attic)and is below the evap it should have a liquid line soleniod at evap that closes when unit satisfies to prevent migration of liquid ref. to condensor. A P trap on suc line is for oil return purposes.

  4. #4
    Originally posted by i b cool
    A P trap on suc line is for oil return purposes.
    But, he doesn't need one on this system. The evap is higher then the compressor... and you don't install them at the compressor (like his dist. told him) anyway.

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