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  1. #1
    Join Date
    Aug 2019
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    Confused problem after problem.. help please

    Okay... got a packaged rooftop heat pump made by Valent. It is quickly becoming my most hated unit. It's running 410a and it uses a copeland digital scroll... the kind with the external unloader solenoid, has VFD everything, and is all controlled by a damn computer...


    Problem 1:
    Found the control system calling for 100% cooling with no temperature drop across the coil. Up to the roof to check it out and found the TXV was starving the indoor coil. [low suction, high superheat, normal discharge and high subcooling]
    pulled the bulb and held it in my hand for about 5 minutes; no change.
    Cool... replace the TXV...

    Problem 2:
    Recharge to factory spec and fire it back up.
    System started to display different symptoms. [400 discharge (this units happy place), maybe 1 or 2 degrees subcooling. 170-180 suction, and i don't recall superheat, compressor trips thermal overload if left running for about 15 minutes].
    System was in override mode and set for 100% cooling, and I found the unloader solenoid was letting hot gas back into the suction line (suction side of the solenoid was discharge level hot)
    Cool... replace the unloader...

    Problem 3:
    I have now replaced the unloader... and this damn system has thrown me another curve ball...
    Symptoms are similar to Problem 2, but definitely a different cause. The unloader is now working normally.
    [in Cooling: 380-385 discharge, 2-3 degrees subcooling, 170 suction, 3-4 degrees superheat, 5 degree drop over the coil if I'm lucky].
    Reversing valve seems fine. Its switching, and there's no measurable temperature change between the ins and outs.
    [In heating (piston): 370ish discharge 2-3 SC, 170 suction, 4-5 SH, just under 20 degree rise across the coil.]
    System will still trip the thermal if left running...


    So... now here we are... If it were a recip compressor, I'd be thinking bad valve(s)... but this is a scroll... I've never seen these symptoms from a scroll... they either work or they don't... and being a digital scroll, I don't want to go replacing something that expensive unless I'm sure...
    There's no isolation valves in the system, so I can't test for pressure bleed-back.
    I can't think of anything else that could cause this problem... so I'm here looking for thoughts, feedback, experience, tips, tricks, premonitions, ceremonial rituals... anything that will help diagnose and/or confirm my thoughts....

    PS-yes, the drier was changed.


    thanks folks

  2. #2
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    31,493
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    People here are going to want more numbers.

    Model and serial.

    Dry and wet bulb.

    What were the numbers after you changed the TEV?

    How long until problem number 2?

    Etc.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist
    Member, IAEI

    AOP Forum Rules:







  3. #3
    Join Date
    Nov 2011
    Location
    East Side
    Posts
    6,712
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    what was your outdoor temp and indoor load? 410 should be running 120/320.....your pressures are pretty high, unless you have high load.

    but your SC and SH are also low.....with these I would expect undercharge.

    I might try to add some charge and see what happens.....your numbers may come in line.

    microchannel coils?

  4. #4
    Join Date
    Dec 2014
    Posts
    2,850
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    What is compressor amp draw? And its relation to the correct amp draw?
    Is this a heat pump? Or is this unit that has reheat?
    Does the compressor open up on the winding temperature or is it opening on the bypass?
    What is the CFM? Is the expansion valve adjustable?

    Sent from my SM-G950U using Tapatalk

  5. #5
    Join Date
    Aug 2019
    Posts
    10
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    Thread Starter
    Valent model
    VPRX-110-8i-10i-C-1DX.
    Serial
    13616960

    Copeland Compressor model
    ZPD91KCE-TFD-250

    Coils are fin and tube

    Indoor is about 75ish. Outdoor is about 80-85.

    Problem 2 occurred immediately after changing the TXV, so those were the numbers.
    Charge was weighed in each time to factory specs which has worked for years.

    400psi head is where this unit throttles its outdoor fan VFD to maintain. That puts me at about 115 SCT... which Im okay with. And its not much lower at 380, so Id be okay with that too if it werent lower than normal for this unit.

    Yes, its a heat pump. No reheat.
    Indoor fan is running normal and moving plenty of air. Didnt get a CFM reading though. And I never got a chance to get an amp reading before the thermal tripped (windings).

    Ill be heading back this afternoon to check it over again.

  6. #6
    Join Date
    Nov 2011
    Location
    East Side
    Posts
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    Whats your discharge superheat?

    Sounds like youre not moving enough dense refrigerant gas through the compressor.

  7. #7
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    8,364
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    Slow the indoor blower vfd and see if that helps the high suction.

    If not, is there hot gas bypass?


    Sent from my iPhone using Tapatalk

  8. #8
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    8,364
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    Is the heat running?

    Does this thing have a heat recovery ventilator?

    Economizer too far open?

    Seems like something must be adding a boat load of heat to the evap.

    With 60 degree evap saturation, the air across the evap would need to be about 90.

    400 discharge seems too high for a internally bypassing compressor.


    Sent from my iPhone using Tapatalk

  9. #9
    Join Date
    Aug 2019
    Posts
    10
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    Thread Starter
    Never got back to it today.
    No heat recovery.
    Econmizer defaults to 40% OA, but Ive tried it at 100% and 0% OA and it doesnt make a difference.

    When I took the readings, air entering the coil was 74, air off the coil was 70. Coil temp was reading 65.

    The 400 psi discharge was recorded when the unloaded was allowing discharge gas back into the suction line. That solenoid has been replaced. Discharge now hovers around 370psi.

  10. #10
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
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    Take an amp draw of the compressor. If its near rated, then its something in the system.

    If its way low, could be the compressor.

    Are you sure the solenoid is in right, and functional?

    What happens if you change the load command lower?

    Its definitely worth trying to add gas.



    Sent from my iPhone using Tapatalk

  11. #11
    Join Date
    Aug 2019
    Posts
    10
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    Thread Starter
    Solenoid is installed correctly and functional. When commanded to drop to 50% capacity, the solenoid opens for 10 seconds and pressures balance out.

    At 100% the outlet of the solenoid is cool to the touch. Not cold, but the same temp as the suction line. So no hot gas is getting through there...

    Also, no hot gas valve. Its a pretty basic system, other than the digital scroll and all the VFDs.

    Ill head there first thing tomorrow and get the compressor amps.

  12. #12
    Join Date
    Aug 2019
    Posts
    10
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    Thread Starter
    I’m now 98.975% sure it’s the compressor.
    It’s rated at 16.2 amps. It’s pulling 11.8. The same model compressor in a neighboring unit pulls the same.
    Discharge pressure is lower than before, on getting to about 365. Suction about 165.
    Discharge pipe temp got a little over 300F before I pulled the plug, while the suction line temp remained fairly constant.
    The most obvious thing though, is the notable hissing noise now coming from the compressor while it’s running.

    I put 2 sets of gauges on the system just to confirm there wasn’t any restrictions or other pressure anomalies.

    So. Any final thought before I go order a compressor? Lol
    Last edited by Dad; 08-23-2019 at 02:25 PM.

  13. #13
    Join Date
    Dec 2014
    Posts
    2,850
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    Quote Originally Posted by beahrdog View Post
    I’m now 98.975% sure it’s the compressor.
    It’s rated at 16.2 amps. It’s pulling 11.8. The same model compressor in a neighboring unit pulls the same.
    Discharge pressure is lower than before, on getting to about 365. Suction about 165.
    Discharge pipe temp got a little over 300F before I pulled the plug, while the suction line temp remained fairly constant.
    The most obvious thing though, is the notable hissing noise now coming from the compressor while it’s running.

    I put 2 sets of gauges on the system just to confirm there wasn’t any restrictions or other pressure anomalies.

    So. Any final thought before I go order a compressor? Lol
    Get out your 3lb hammer and clobber that compressor head on the side. You may just be able to reseat that valve the bypass valve. If not I think the last compressor I changed about that size was not nearly three grand. Maybe 50% of that?

    Sent from my SM-G950U using Tapatalk
    Last edited by Dad; 08-23-2019 at 02:25 PM.

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