Virginia Envision split unit High Pressire Lockout

Discussion in 'Maintenance and Troubleshooting' started by geome, Aug 23, 2019.

  1. geome

    geome Member Forum Leader

    Hi Everyone! It's been a while since I posted. For 10 years, our systems have been running great. For the past 2 days, we have been experiencing High Pressure lockouts after several hours of running.

    It is still to be determined if the 2 Grundfos circulation pumps (UP 26 99) are ok. They "feel" normal, but I recall that feeling the pumps are not the best way to determine if they are functioning correctly. We have 3,000 feet of horizontal closed loop with 4' average depth in SW Virginia. This split unit shares this loop with a 3 ton packaged unit. There is methanol in the loop for freeze protection, however I do not recall the percentage.

    So far, the installer has replaced a 35 microfarad capacitor that was reading 30. He should be back out today.

    Split unit model number NDZ026A11AC, serial number 090400xxx

    I ran the unit for 50 minutes this morning as a test to get the following readings:

    EAT 68.0 F
    LAT 47.0 F

    Loop In 39.5 PSI
    Loop Out 35.2 PSI

    Loop Temp In 82.9 F
    Loop Temp Out 88.7 F

    What do you believe the problem might be?

    Thank you!
    P.S. I failed to mention that there are no Comfort Alert errors.
    P.P.S. Tested at full load and DSH "On"
    P.P.P.S. The 3 ton unit has not locked out even though it shares the same loop as the split unit. The loops are not throttled to each unit (i.e. they are wide open.)
    Last edited: Aug 23, 2019
  2. geome

    geome Member Forum Leader

    I just recorded the following with the DSH off:

    EAT 71.0 F
    LAT 53.0 F

    Loop In 39.1 PSI
    Loop Out 35.1 PSI

    Loop Temp In 83.3 F
    Loop Temp Out 90.5 F

    Using the Pressure Drop table from Water Furnace, I figure about 8 GPM flow. So, this doesn't seem to be a flow issue, unless I figured something wrong...

    Any ideas?
    Last edited: Aug 23, 2019
  3. geoxne

    geoxne Active Member Forum Leader

    High pressure faults in cooling are most commonly due to lack of water flow. Yes, your DeltaP looks good and GPMs calculated are good. So, unless something is flaky with your pump dropping out when your not looking or when other unit is running.-
    -Bad high pressure switch or wire onnection
    -scaled or obstructed water coil (unlikely in a closed loop system that was properly purged and flushed) An obstructed coil will mimic a proper flowing DeltaP but with less water flow)
    -TXV sticking or bad (in airhandler in cooling mode) make sure sensing bulb is placed correctly, secure and insulated.
    -Possible overcharge

    Try running with other unit off and see if you get similar numbers. Maybe the unit acting up isn't calling the pump due to a loose connection??? Look for simple stupid stuff first.
  4. geome

    geome Member Forum Leader

    Thanks geoxne. Good ideas. Here is some additional information.

    The packaged unit wasn't running when I took the readings this morning. On the flip side, should I get new readings with both units running? A loose electrical connection to one of the pumps or whatever signals them to come on could be possible. I'll suggest they check this. Both pumps are designed (unfortunately, from an efficiency standpoint) to turn on together.

    The charge has not been physically checked or adjusted since the unit was put in service (10 years.) Could it be high?

    I'll ask them to check for a bad high pressure switch and wiring and the TXV as you mentioned.

    I'll mention the obstructed water coil possibility too, but there have been no loop changes since the unit was new other than me adjusting loop pressure as needed every 2 -3 years. I purge air from the hose and adjustment tool before inserting it into the PT valve so as not to introduce air into the loop.

    Please let me know if you or anyone else thinks of anything else to check.

    Lockouts that can't be immediately duplicated stink. :-(

    Thanks again!
  5. geoxne

    geoxne Active Member Forum Leader

    If water coil was obstructed then your water side DeltaT would be high with LWT approaching 120F or more to trip. It is not (at least at the time recorded).
    I doubt it.
  6. geome

    geome Member Forum Leader

    After taking pressures, the tech said the TXV was bad. The pressure was at 340 and still climbing when he went into the attic and detached the sensor bulb. Then the pressure dropped to normal. I should note that the air handler is a 10 year old Carrier.

    He said that some people leave their units like this. What impact does this have on efficiency? I assume I should either replace the TVX or replace the TVX with the coil as a unit? What do you recommend? I want the system to be reliable.

    Should the TVX have lasted longer than this?

    Any suggestions on how to try to get Carrier to cover this since the unit is only 4 months out of warranty?

    Thank you!
    Last edited: Aug 27, 2019

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