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Head pressure

I work on r410a system(txv) today! My head pressure run 425 psig with 0 subcooling and my low side ( back pressure) only run 105 psig my suction line 72f ( I got 38 superheat)
I test txv sensing bulb into hot water it did react, I put temperature pro cross filter drier inlet and outlet no pressure drop, I couldn’t figure out today
anyone got any opinion? Thanks

Comments

  • mattmia2
    mattmia2 Member Posts: 6,688
    Sounds undercharged but i'm not the expert on this.
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,881
    72 suction line? How’s your airflow?
    steve
  • mattmia2
    mattmia2 Member Posts: 6,688
    Do you have ice on like the bottom 1/4 of the evaporator?
  • JOutterbridge
    JOutterbridge Member Posts: 13
    edited July 22
    I work on r410a system(txv) today! My head pressure run 425 psig with 0 subcooling and my low side ( back pressure) only run 105 psig my suction line 72f ( I got 38 superheat)
    I test txv sensing bulb into hot water it did react, I put temperature pro cross filter drier inlet and outlet no pressure drop, I couldn’t figure out today
    anyone got any opinion? Thanks
    Standard split system? If the TXV reacts the sensing bulb could be going bad or your txv is underfeeding. I had the same issue a week ago with the high side 475 and lo side 50 and slowly dropping. If your airflow is correct most likely a txv restriction or sensing bulb issue.
  • ratio
    ratio Member Posts: 3,292
    Zero subcooling means there's no liquid refrigerant packed up in the condenser. High head pressure means there's either an obstruction downhill from the condenser or no heat leaving the condenser. High superheat means the TXV can't feed enough liquid to bring the superheat down, which goes along with no liquid making it to the valve. Assuming indoor & outdoor conditions aren't crazy, dirty condenser coil. What's the approach temp?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,664
    dirty condenser, Add a little charge and see what the superheat does. Could be a bad txv. Non condensable in the system
  • johnjohn89
    johnjohn89 Member Posts: 65
    ratio said:
    Zero subcooling means there's no liquid refrigerant packed up in the condenser. High head pressure means there's either an obstruction downhill from the condenser or no heat leaving the condenser. High superheat means the TXV can't feed enough liquid to bring the superheat down, which goes along with no liquid making it to the valve. Assuming indoor & outdoor conditions aren't crazy, dirty condenser coil. What's the approach temp?
    What is approach temp means? Approach temp is for chiller right?
  • ratio
    ratio Member Posts: 3,292
    Approach temp is the difference between the liquid line temperature & the outdoor air temperature. In other words, if your liquid line temp was 100° & the outdoor air temp was 90°, your approach would be 10°. IIRC New Lennox charge by approach & not subcooling.

    In any case, I'm being you have high approach.

  • johnjohn89
    johnjohn89 Member Posts: 65
    ratio said:
    Approach temp is the difference between the liquid line temperature & the outdoor air temperature. In other words, if your liquid line temp was 100° & the outdoor air temp was 90°, your approach would be 10°. IIRC New Lennox charge by approach & not subcooling.

    In any case, I'm being you have high approach.

    Thank u my mentor haha
  • johnjohn89
    johnjohn89 Member Posts: 65
    @all thank u for the helping 
  • pecmsg
    pecmsg Member Posts: 3,339
    ratio said:
    Approach temp is the difference between the liquid line temperature & the outdoor air temperature. In other words, if your liquid line temp was 100° & the outdoor air temp was 90°, your approach would be 10°. IIRC New Lennox charge by approach & not subcooling.

    In any case, I'm being you have high approach.

    I’m used to “Approach” being used on Water cooled units. Lennox now wants that information?
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,288
    edited July 25
    As all of you Approach retirement, the doctor may want to take your temperature just in case you have a fever. Hope it's not Covid!
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

    pecmsg
  • ratio
    ratio Member Posts: 3,292
    pecmsg said:

    I’m used to “Approach” being used on Water cooled units. Lennox now wants that information?

    That's what my li'l buddy said, charge to an approach of whatever. A couple of caveats: these are commercial condensers (10-15 ton) & that's what he told me, I haven't actually verified it myself.

    As long as the outdoor coil's clean, it should work.