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  1. #1
    Join Date
    Oct 2019
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    HELP...An Odd Problem that None of My Subs can figure out... Compressor issues.

    Hi All, I'm new to the forum and having a problem that is a causing some big headaches with a client (I'm a GC). I'm just so lost right now.

    I have a client that wanted to rehab a house to live. When we got in there, the owner told us that the previous owner replaced that both AH and AC 2 years prior but the house sat empty for those 2 years (3 ton, off-brand Carrier unit). After our work, we fired up the units and they seems to run and cool well.

    We received a call a few days after the owners moved in that the outside unit was making a humming noise and vents were blowing warm (I have a video). A sub contractor went but the machine was working fine and he installed a hard start in the event the comp was struggling to start. The client then called again and said the machine continued to hum but when restarted, it would work. However, at times, the compressor didn't start at all (fan blow only -- over heat).

    These are 2 faults that continue to this day... and sporadically every time I go the machine is cooling well and compressor behaves. : Either 1. The compressor struggles to start and makes a loud hum sound. or 2. Compressor doesn't start, only fan runs and compressor temp is overheated and can restart by cooling down compressor.

    This problem continued with multiple subs trying different things. One sub said the compressor was bad, and it was replaced under warranty. SAME THING HAPPENED with the new comp. Another sub replaced contactor, capacitor, and other sub played with the amount of gas. SAME

    FINALLY, the homeowner decided he wanted to CHANGE the unit. My sub calced the square footage of the home and decided a larger unit was needed. A 5-ton Rheem was installed with new wiring and piping. More venting was created. We even had the electric line monitored by the local power company to ensure that wasn't any issue with either of the phases that run to the house. AND STILL THE SAME PROBLEMS INTERMITTENTLY occur. Once a day or once every 2 days.

    I replacement the electric panel, thermostat.... and I can't think of anything else. I'm being threatened with a law suit as my sub was the one that talked them into the larger unit.

    I have brought different subs (4 in total) and no one can figure it out. Most recently, a balance test and CFM test were done and this contractor said the machine wasn't moving enough air. My first that was that this wasn't the issue cause I would think the machine would start to freeze.

    I'm 10000% LOST and losing money like no other. I have more details if needed.... sorry for the winded post.

  2. #2
    Join Date
    Aug 2002
    Location
    Southold, NY
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    From 3 tons to 5 tons and its moving enough air?

  3. #3
    Join Date
    Jun 2012
    Location
    Northern NV
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    Happen at the same time each day?

    And..... bad move allowing someone to replace a 3T with a 5T as this generally compounds the issue.

    Are there no qualified A/C techs in your 'hood?

  4. #4
    Join Date
    Oct 2016
    Location
    Clearwater, Florida
    Posts
    1,439
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    Wow.

    That's quite something.

    Is it a 3 phase compressor or single phase? I'm guessing it's single if it has a start capacitor.

    The only reasons a compressor won't start is,

    A: it's locked up.
    B: It's got no power or not enough.
    C: The capacitor is bad and it can't get it's "Kickstart"
    D: An incomplete circuit, which would be compounded to B.
    E: Intrenal safety went off.

    There's not much else, you can get into details of why each point is what it is, but there's not much else.

    Did you get new T-stat wire pulled when the new unit went in? A Licensed electrician once beat into my skull so thoroughly and made me repeat it about 100 times that an intermittent problem is ALWAYS a loose connection.

    You replaced all the hardware when a new unit showed up, could be it's short cycling on the extreme, compressors don't like that and it will wear it out really, really fast, a loose wire or a semi broken wire can do that, it'll make a connection, break it, make it, break it, etc.

    Ohm out each wire from the T-stat to the condensing unit, it's gotta be something OTHER than what you've replaced so far, so find out EXACTLY what the subs did, each one, and make a list, post that list here and I'm sure we can tell you what else needs checking.

    My first thought is bad wiring and severe short cycling, that's the only thing making any sense considering the problem hasn't changed at all.

  5. #5
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    3,141
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    Is this thing running off of a Nest thermostat?

    Just a hunch.

    My second guess is that the home owners are crazy and the noise is coming from something else. Maybe a sump pump?

    My third guess would be that this is a heat pump and when you say warm air is blowing out of the vents, the unit is actually going into heating mode and it's the reversing valve that's humming. Or perhaps they are running it in heating mode on purpose and it's going into defrost periodically and doing what it's supposed to. Could it be that the thermostat has an "auto" mode to switch between heating and cooling automatically, and it's bouncing back and forth? Maybe the stat is in a dumb place with a vent blowing on it or a light bulb is pointed at it or it's too close to something else that produces heat?

    Either way, I agree with the others that imply that it was probably nuts to go with a larger unit.

    Most ducts are undersized from the start for whatever system a house originally comes with. I know you said they added more vents, but it would take a considerably larger duct system to go from 3 tons to 5. Hopefully whoever did this knew what they were doing and has some real load calcs to back it up.

    Good luck!
    Last edited by ammoniadog; 10-21-2019 at 06:55 PM.

  6. #6
    Join Date
    Jun 2014
    Location
    Dover, DE
    Posts
    11,357
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    Please post the commissioning report for this unit that was just installed
    I havent failed. Ive just found 10,000 ways that wont work. - Thomas Edison

    Its not whether you get knocked down, its whether you get up. - Vince Lombardi

    "In this house we obey the laws of thermodynamics" - Homer Simpson

    Local 486

  7. #7
    Join Date
    Jun 2003
    Location
    Texas
    Posts
    1,432
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    hire a qualified sub

  8. #8
    Join Date
    Dec 2007
    Posts
    9,104
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    Manual J
    Manual D

    Model and serial number of the old equipment, if available, and the new equipment.

    House size and location if neither of the above(but should have that if the sub "calced" it).

    Most likely oversized equipment on undersized ducts.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    77,999
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    When you say only the fan runs. Do you mean the indoor fan, or the outdoor fan?

    We’re the low voltage wires from the thermostat to the out door unit replaced ?
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Mar 2018
    Location
    Chico, Ca #StateofJefferson
    Posts
    1,337
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    Agree with previous posts about your low voltage side. I would be getting a proper commissioning report written up from the installing company showing the refrigerant charges and airflow are correct for your records as I think in all likelihood enlarging the system by 60% is going to create an S-storm of problems. Get a copy of their completed load calculations as well
    Last edited by Makeitcold; 10-23-2019 at 01:52 AM.

  11. #11
    Join Date
    Oct 2019
    Posts
    5
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    Thread Starter
    Quote Originally Posted by ammoniadog View Post
    Is this thing running off of a Nest thermostat?

    Just a hunch.

    My second guess is that the home owners are crazy and the noise is coming from something else. Maybe a sump pump?

    My third guess would be that this is a heat pump and when you say warm air is blowing out of the vents, the unit is actually going into heating mode and it's the reversing valve that's humming. Or perhaps they are running it in heating mode on purpose and it's going into defrost periodically and doing what it's supposed to. Could it be that the thermostat has an "auto" mode to switch between heating and cooling automatically, and it's bouncing back and forth? Maybe the stat is in a dumb place with a vent blowing on it or a light bulb is pointed at it or it's too close to something else that produces heat?

    Either way, I agree with the others that imply that it was probably nuts to go with a larger unit.

    Most ducts are undersized from the start for whatever system a house originally comes with. I know you said they added more vents, but it would take a considerably larger duct system to go from 3 tons to 5. Hopefully whoever did this knew what they were doing and has some real load calcs to back it up.

    Good luck!
    YES... it is on a Nest. Curious as to why you asked that?

  12. #12
    Join Date
    Oct 2019
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    5
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    Thread Starter
    Quote Originally Posted by beenthere View Post
    When you say only the fan runs. Do you mean the indoor fan, or the outdoor fan?

    We’re the low voltage wires from the thermostat to the out door unit replaced ?
    I meant outdoor, sorry. Actually, no, LV was not replaced. Seems like you have a hunch about something.,,,, maybe??

  13. #13
    Join Date
    Oct 2019
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    5
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    Thread Starter
    Quote Originally Posted by Olivero View Post
    Wow.

    That's quite something.

    Is it a 3 phase compressor or single phase? I'm guessing it's single if it has a start capacitor.

    The only reasons a compressor won't start is,

    A: it's locked up.
    B: It's got no power or not enough.
    C: The capacitor is bad and it can't get it's "Kickstart"
    D: An incomplete circuit, which would be compounded to B.
    E: Intrenal safety went off.

    There's not much else, you can get into details of why each point is what it is, but there's not much else.

    Did you get new T-stat wire pulled when the new unit went in? A Licensed electrician once beat into my skull so thoroughly and made me repeat it about 100 times that an intermittent problem is ALWAYS a loose connection.

    You replaced all the hardware when a new unit showed up, could be it's short cycling on the extreme, compressors don't like that and it will wear it out really, really fast, a loose wire or a semi broken wire can do that, it'll make a connection, break it, make it, break it, etc.

    Ohm out each wire from the T-stat to the condensing unit, it's gotta be something OTHER than what you've replaced so far, so find out EXACTLY what the subs did, each one, and make a list, post that list here and I'm sure we can tell you what else needs checking.

    My first thought is bad wiring and severe short cycling, that's the only thing making any sense considering the problem hasn't changed at all.
    Great info.... BUT NO, they didn't pull a new T-stat!!!! What's your thinking there? And it was on a NEST as well. I will OHM out the wires.

    I'm not too familiar with short-cycling. Is the potential bad-wiring the cause or the effect?

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