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  1. #1
    Join Date
    Jul 2007
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    Virginia
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    Compressor pump down - high pressure trips

    R410a with TXV - After a 4" spacer was installed between my evaporator and furnace, the tech added a little 410a, but I suspect he overcharged. Subcooling is about 17F (nameplate calls for 15F, so its within 3F).

    But when I had another tech do a compressor pumpdown test for me, the following happens:

    suction pressure starts to drop, hi side pressure starts to drop, but the high pressure trips the unit offline rather quickly (suction only gets down to 150, high side gets down to 200).

    I assume that high pressure sensor is on the other side of the king valve, so I guess we aren't really seeing the pressure between the compressor discharge and the king valve.

    Is this a symptom of over-charge? It does not trip during normal operations.

    I've got another company coming out next week to do a full check of this system, but I wanted to check my logic.

    thanks.

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    6,465
    You sure it's not the low pressure switch cutting it off?

  3. #3
    Join Date
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    Quote Originally Posted by jtrammel View Post
    You sure it's not the low pressure switch cutting it off?
    Yea, its a Carrier Infinity, so I can see it logged on the controller interface. Suction pressure is about 150psi when it trips, so its not even close to the set point of 50psi for low pressure cutout.

  4. #4
    Join Date
    Oct 2010
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    Anderson, South Carolina, United States
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    6,465
    It may be overcharged, the condenser should have the capacity to hold entire charge in most cases. Unless it has oversized or abnormally long line set.

  5. #5
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    Sep 2008
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    Western PA
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  6. #6
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    Feb 2009
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    Tallahassee, FL
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    No carrier is not Microchannel.

    Might be time to have the charge recovered and weighed to see just how much is in there.

    That would be a good time to have true discharge pressure tap added to get total pressure read.

  7. #7
    Join Date
    Sep 2008
    Location
    Western PA
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    25,426
    Quote Originally Posted by SBKold View Post
    No carrier is not Microchannel.

    Might be time to have the charge recovered and weighed to see just how much is in there.

    That would be a good time to have true discharge pressure tap added to get total pressure read.
    I'm not familiar with the various brands of equipment, just know that microchannels are more sensitive to excess charge.

    I agree that it is time to pull the charge and see where it stands.

  8. #8
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    Western PA
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  9. #9
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
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    Good point jp. Recovering and bottle the freon should reveal overcharge and/or noncondensibles.

    I really hope someone would not install a high end infinity and not pull a vac but you never know.

  10. #10
    Join Date
    Mar 2009
    Location
    Mid-Mo
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    3,594
    Interesting, agreed with everyone else's thoughts. I worked on my first infinity yesterday and I was impressed at how advanced it was but in the same breath how simple it was to work on. Of course the problem was a dead capacitor.

  11. #11
    Join Date
    Sep 2011
    Posts
    58
    Quote Originally Posted by rogressem View Post
    R410a with TXV - After a 4" spacer was installed between my evaporator and furnace, the tech added a little 410a, but I suspect he overcharged. Subcooling is about 17F (nameplate calls for 15F, so its within 3F).

    But when I had another tech do a compressor pumpdown test for me, the following happens:

    suction pressure starts to drop, hi side pressure starts to drop, but the high pressure trips the unit offline rather quickly (suction only gets down to 150, high side gets down to 200).

    I assume that high pressure sensor is on the other side of the king valve, so I guess we aren't really seeing the pressure between the compressor discharge and the king valve.

    Is this a symptom of over-charge? It does not trip during normal operations.

    I've got another company coming out next week to do a full check of this system, but I wanted to check my logic.

    thanks.
    Sounds like superheat is at a good point if its 17 and the name plate calls for 15.
    I don't think that the compressor tripping during a pump down would mean it's overcharged, (hp switch) is just protecting it, is there no way to override it via the contactor so you can complete the pump down process?

  12. #12
    Join Date
    Oct 2008
    Location
    Indianapolis
    Posts
    172
    Quote Originally Posted by rogressem View Post
    R410a with TXV - After a 4" spacer was installed between my evaporator and furnace, the tech added a little 410a, but I suspect he overcharged. Subcooling is about 17F (nameplate calls for 15F, so its within 3F).

    But when I had another tech do a compressor pumpdown test for me, the following happens:

    suction pressure starts to drop, hi side pressure starts to drop, but the high pressure trips the unit offline rather quickly (suction only gets down to 150, high side gets down to 200).

    I assume that high pressure sensor is on the other side of the king valve, so I guess we aren't really seeing the pressure between the compressor discharge and the king valve.

    Is this a symptom of over-charge? It does not trip during normal operations.

    I've got another company coming out next week to do a full check of this system, but I wanted to check my logic.

    thanks.
    You are correct on the location of the HP sensor and the reason you are not seeing the HP on gauge.

  13. #13
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Quote Originally Posted by rogressem View Post
    I've got another company coming out next week to do a full check of this system, but I wanted to check my logic.
    Tell them to bring a compressor with them!
    It is ridiculous that your problem has persisted for this long, at least 2 or 3 years.

    As for cutting out on high pressure while pumping down, it just means the system contains more refrigerant than the condenser can hold. It could be over charged, or it could just be a longish line set.
    If you have a long refrigerant line set, 50+ feet, charging the system to a couple of degrees more subcooling than the name plate calls for may be ok, often even called for in the manufacturers instructions.
    If more government is the answer, then it's a really stupid question.

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