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  1. #1
    Join Date
    Nov 2010
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    Central Florida
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    555

    Knocking in new air handler?

    Anybody know what might be causing a knocking sound from a new air handler when the outside condensor shuts off? Doesn't seem to matter whether the blower is shutting off, or going from high to low speed, the common denominator seems to be when the condensor shuts off. The sound last about 3 seconds and seems as if it might be coming from where the lineset connects to the handler. Or possibly even the linset itself? Carrier Comfort series heat pump.

    Any thoughts or test-tips would be appreciated, am just trying to narrow it down further before calling the dealer.

    Thanks,

    Sonic

  2. #2
    Join Date
    Dec 2010
    Location
    Down by the river
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    1,579
    explain the noise better, metal to metal ting, or like someone knocking on door.

  3. #3
    Join Date
    Nov 2010
    Location
    Central Florida
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    555
    Tough to describe....hmmm.... I'm going to have to listen more closely tonight and reply later because no description is coming to mind. But I'd say it's closer to a knock on a door than a ting.

    I did call the dealer and they are sending somebody out tomorrow but he did mention "maybe it's a TXV valve" .... (or something like that). Isn't that a part that can go bad if an R22 lineset flush is not done properly? LoL

    It should be a warmer day tomorrow in the mid/upper 70's so the tech is going to check my Puron level then as well to make sure it's right. If there is anything else I should ask that he check while he's there please let me know.

  4. #4
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    Dec 2010
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    Down by the river
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    sounds more like the trap drying up due to low humidity and the air sucking water up, out of trap and drain line, then the weight drops it back and sounds like a mild knock, or glunk, if thats a descriptive word.

  5. #5
    Join Date
    Nov 2010
    Location
    Western Mass
    Posts
    21
    Quote Originally Posted by Southern Mech View Post
    sounds more like the trap drying up due to low humidity and the air sucking water up, out of trap and drain line, then the weight drops it back and sounds like a mild knock, or glunk, if thats a descriptive word.
    Wouldnt that be when the blower shuts off or turns on? Could be pipeing connections up against something/solidly mounted. As far as the txv it is not going to produce the noise itself they dont move that fast or have big enough parts to do such a thing. Maybe the pipes are hitting on sheet metal/vibrating? Noises are tough to diagnoise without hearing them. Id deffnitly make sure he dose a proper superheat and subcooling calc. though. IF it was slugging liquid at the compressor that could cause some serious rattling, which may not be the techs fault as it could be a bad txv causing this too.

  6. #6
    Join Date
    Dec 2006
    Location
    Litchfield,Il
    Posts
    565
    Are you sure its coming from the AHU? Maybe its coming from outside. Would if your Condenser fan is hitting something.

    Would if your Evap. coil is frosting up and you hear it thawing out . Let us know the outcome.

  7. #7
    Join Date
    Dec 2010
    Location
    The Colony, TX.
    Posts
    15
    check for a shipping bracket i had a problem from a customer who had a differant company do her new installation and they forgot to take out the shipping bracket. the bracket is mounted to the blower housing and and is to be removed and if it is not then when the blower comes on than it will make a knocking sound for a few sec. and when the blower moters rpms rev up the sound will go away and come back. not all models have this shipping bracket but its worth a try. if not call the company who did the install and make them take care of the issue.

  8. #8
    Join Date
    Dec 2005
    Posts
    1,829
    Quote Originally Posted by SonicExplorer View Post
    Anybody know what might be causing a knocking sound from a new air handler when the outside condensor shuts off? Doesn't seem to matter whether the blower is shutting off, or going from high to low speed, the common denominator seems to be when the condensor shuts off. The sound last about 3 seconds and seems as if it might be coming from where the lineset connects to the handler. Or possibly even the linset itself? Carrier Comfort series heat pump.

    Any thoughts or test-tips would be appreciated, am just trying to narrow it down further before calling the dealer.

    Thanks,

    Sonic
    Did you call the contractor and ask them if they are missing an installer ?

  9. #9
    Join Date
    Apr 2008
    Location
    TEXAS
    Posts
    1,701
    sounds like somebody had their lines flushed!
    "When the people find they can vote themselves money,that will herald the end of the republic" - Benjamin Franklin

    "Government is not reason, it is not eloquence, it is force;like fire, a troublesome servant and a fearful master. Never for a moment should it be left to irresponsible action"- George Washington

  10. #10
    Join Date
    Nov 2010
    Location
    Central Florida
    Posts
    555
    Smitty, are you a natural born jackass or do you have to work at it? ;-)

    Still trying to narrow the problem down but here's a few more details:

    The noise does sound like a line knocking against something inside the handler, that's the best way I can describe it. It's not a metal-on-metal sound but like a line knocking against something non-metalic. The kocking becomes more rapid as it diminishes. The smaller line can be felt as clearl vibrating at the air handler when this occurs. Again, this is when the condensor outside shuts off, doesn't matter the fan speed of the handler either. When the condensor shuts off the knocking in the handler happens for a few seconds. Doesn't ALWAYS do it, but usually. And I have only been running heat by the way if that gives any clues.

  11. #11
    Join Date
    Nov 2010
    Location
    Central Florida
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    555
    Further investigation, it does indeed appear to be the smaller line going into the handler. Why, or what is actually occuring, is beyond me. I did however read in the Carrier manual and it says the condensors are charged for a 15 foot lineset, and with mine around 33 feet, that makes it probably about 10-12oz undercharged. Which might also explain why the system is not heating as well as my previous 16 year old one. I'm getting KILLED by the aux heat with this VisionPro stat. I've used TWICE as much electricity in the last 24 hours as I EVER have before. That stupid stat, for all the intelligence, apparently doesn't have any programming that deals with aux heating conditions. It just makes up it's own mind. Need to look into it more but I think Aux heat can be locked out by attaching another temperature sensor - but it's rediculous that I'd need to do that. There should be a way to simply specifiy a temperature drop where if it hits that level the aux heat kicks on to assist.

  12. #12
    Join Date
    Nov 2010
    Location
    Central Florida
    Posts
    555
    If there was air in the lines, or the Puron level was too low, would either of those conditions possibly be the cause of the knocking/vibration in the lineset at the handler when the outside condensor turns off?

  13. #13
    Join Date
    Dec 2010
    Location
    Down by the river
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    1,579
    more likely you are hearing liqued rush and then a void of liquid, kinda like a hose full of water then an air bubble goes though.

    I know where you are comming from and a unit charged for 15 ft and a lineset of 33. I have a unit in my own house that does this and I know it's charged right, yours may go away when it gets charged.

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