Results 1 to 12 of 12
  1. #1
    Join Date
    Oct 2009
    Location
    Aust
    Age
    39
    Posts
    49
    Rep Power
    0

    Hammer sound at FCU TXV



    Ok so i have a residential ducted heat pump system that has a TXV at the FCU & at the COND unit (both valves have a built in one way bypass or check valve eg on heating mode the TXV at the FCU is bypassed and reverse for cool mode).

    This unit runs fine on cooling but when switched over to heating and ran for around 1 hour a loud hammering sound is coming from the TXV at the FCU and the pressure on my liquid line is bouncing around like crazy.

    I can't seem to figure out the cause of this issue, below is the steps i have taken so far along with some pressures temperatures i took on my last visit.

    The system is a Unico small ducted system.

    1) Pump down then flush lines & FCU with dry nitro
    2) Verify the TXV is the correct tonnage both FCU & COND
    3) Verified the system has the correct airflow
    4) Change FCU TCV
    5) Install bi flow liquid line drier & sight glass as the system didn't have these originally

    After installing the drier the sound is much much quieter and takes longer to appear than previously.

    Cond one way valve installed? Yes standalone/external
    Cond Capacity 14kW
    Filter drier & sightglass installed at FCU? Yes
    FCU TX Valve CBBIZE-4 16A B15 16110 ZGA 45
    Hot gas pipe at FCU 60degC
    Discharge Temp 52degC
    Discharge Pressure 380PSI
    Liquid line temp at outdoor 31.2degC
    Liquid line temp as it leaves FCU TXV 35degC
    Liquid line pressure 400PSI
    Subcooling on COOL mode 2deg
    Superheat in HEAT mode 5degC
    Suction pressure 100PSI
    Suction Temp 5degC
    FCU amps on HIGH 4.58
    Number of Outlets 25
    Supply Air Temp 41.4degC
    Return Air Temp 18.3degC
    Outdoor Ambient Temp 12degC
    Average airflow per outlet 45l/s
    Airflow l/s 1117 or 2366CFM

    Any help you could provide would be much appreciated



  2. #2
    Join Date
    Nov 2008
    Location
    australia
    Posts
    136
    Rep Power
    16

    Re: Hammer sound at FCU TXV

    Hey mate,
    Have seen this problem in York ducted splits roughly the same kw rating, Unico make a few different units and badge them with other brands. One York unit had an accurator and on heating had low suction pressure as above. did exactly what you did pulled every thing down flushed out replaced but to no avail on 3 units. also look to see if the copper pipes are fixed properly causing hammering I have seen that as well. filters clean I take it, both out door fans running on heating? are both txv's in correct direction and are one way valves in correct direction? 25 registers sounds a lot.

  3. #3
    Join Date
    Oct 2009
    Location
    Aust
    Age
    39
    Posts
    49
    Rep Power
    0

    Re: Hammer sound at FCU TXV

    Thanks for the reply mate.

    The pipes cannot be accessed unfortunately as they run between floor joist I didn't do the install lol.

    The noise only begins in heat mode after it has been running for a few hours, the reason there are so many outlets is it's a Unico small ducted system Model 4860 which specifies a minimum of 24 outlets.

    Funny thing is that there are 2 of these systems in the same house & one runs trouble free whilst the other makes this hammering sound.

    The sound seems to be emanating from the txv & is unlike the humming sound heard on some heat pumps from the discharge being dumped straight into the suction line.......

    Any care to chime in?

  4. #4
    Join Date
    Nov 2008
    Location
    australia
    Posts
    136
    Rep Power
    16

    Re: Hammer sound at FCU TXV

    just a thought could the compressor be worn out and not pumping properly. try and pump it down

  5. #5
    Join Date
    Oct 2009
    Location
    Aust
    Age
    39
    Posts
    49
    Rep Power
    0

    Re: Hammer sound at FCU TXV

    Thanks for tsing the time to reply mate but the compressor pumps down perfectly

  6. #6
    Join Date
    Apr 2010
    Location
    england
    Age
    51
    Posts
    297
    Rep Power
    14

    Re: Hammer sound at FCU TXV

    the one way valve ? or non return lol if its worn it may have broken inside have had that and its a bugger to pinpoint is there a solanoid valve have had this when some muppet fitted one wrong way the txv should shut completly so no flow if its passing could be faulty have had liquid hammer or shock wave when solaniod valve to far from tev on supermarket packs it opens and the shock wave is amazing mkes a 30metre liq line wobble

  7. #7
    Join Date
    Oct 2009
    Location
    Aust
    Age
    39
    Posts
    49
    Rep Power
    0

    Re: Hammer sound at FCU TXV

    Well the funny thing is i have replaced the TXV at FCU (the TXV has an internal non return valve).

    Thanks for all the suggestions so far.

  8. #8
    Join Date
    Nov 2008
    Location
    australia
    Posts
    136
    Rep Power
    16

    Re: Hammer sound at FCU TXV

    what about the tev on outside unit could be hunting causing it to open and shut quickly causing a hammer through the pipes. try putting a wag soaked with hot water on outdoor tev to drive it open all the way open and see what that does. good luck

  9. #9
    Join Date
    Mar 2011
    Location
    Singapore
    Posts
    212
    Rep Power
    16

    Re: Hammer sound at FCU TXV

    Is there any distributor after TXV? if so please insulate the distributor with sticky thick insulation (below).

    Insulatio-300x300.jpg

  10. #10
    rinusg's Avatar
    rinusg Guest

    Re: Hammer sound at FCU TXV

    Hi,
    I run tech support for Unico Inc. over in the UK. There should only be one TXV's in the circuit, common mistake over here as Unico ship the coils with a TXV included in case they get used with Cond. unit without onboard expansion. Remove TXV in the AHU, extend liquid line to back of distributor and all should be well.
    I would say the unit is most likely going to freeze up if not an inverter cond. unit with coil monitoring probes as 24 outlets are not enough for a 4860. You should expect to see about 36 outlets on this size system, 6 outlets per 3.5kW.
    Rinus

  11. #11
    Join Date
    Oct 2009
    Location
    Aust
    Age
    39
    Posts
    49
    Rep Power
    0

    Re: Hammer sound at FCU TXV

    thanks for the reply rinusg but the problem was solved by doing a complete reclaim & recharge, i assume the refrigerant was contaminated

    How did you work out the unit does not have enough outlets? 14kW outdoor.

    14kw/3.5 = 4
    4 x 6 = 24

    Can you please elaborate on why the unit should have only 1 txv?

    This system is reverse cycle and has a one way valve fitted around each TXV so only 1 TXV is metering at any one time whilst the other TXV is bypassed.

    Love to here your thoughts

  12. #12
    Join Date
    Mar 2011
    Location
    Singapore
    Posts
    212
    Rep Power
    16

    Re: Hammer sound at FCU TXV

    Even in VRF VRV some bigger capacity units are using 2 linear expansion valves in order to have quick balance evaporation process for cooling coil, design have sort of two primary and secondary coils (two circuits). All based on engineering research and design to gain the optimum capacity. Some smaller inverter series have 2 expansion and 2 cap-tube in parallel, quite similar to your idea like one stand by or bypassed or fixed opening back up.
    If your system can handle these program or you can design/logic and interlock with respective temperatures to have your TXV to react. while TXV-A is metering TXV-B will act nothing but bypassed, TXV-A broken, auto TXV-B take over and so on.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •