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Low suction pressure normal superheat

Hello to all,
I am working on a ten year old residential split AC system with a TXV located in a finished basement that has worked fine until now. The system actually works fairly well even on hot days, its just 2-3 degrees off the thermostat setting. The suction pressure is 95 PSI, about 28 degrees, but the superheat is normal, at 10. The liquid line pressure is fine, the outside coil is clean and the subcooling is 10, which is what the manufacturer calls for. I changed the TXV but did not have any improvement. The only thing I can think of is a dirty evap coil. I just cant see that being the problem with a normal superheat and no icing of the coil.
Any suggestions would be appreciated.


  • RPK
    RPK Member Posts: 95
    What is the airflow and what is the return air temperature? This sounds like low load. Cleanliness of coils and proper airflow should be confirmed before trying to diagnose the refrigeration sue of things. 
  • ChrisJ
    ChrisJ Member Posts: 14,085
    I assume this is a 410A system?
    R22 that pressure would be on the warmer side.

    Why did you change the TXV if the superheat is correct?
    If it's not icing up perhaps your measurements are off? Is there any sign of frost at all on the evaporator?
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    EBEBRATT-Ed Member Posts: 13,334
    Although frost and Ice can occur any time the evap drops below 32 deg, with air moving across the evap you can usually get down to around 25 deg before icing up.

    Sounds line a dirty evap, plugged filter, low air flow, dirty blower wheel etc.

    Check supply and return temp and temperature split
  • charliechicago
    charliechicago Member Posts: 124
    Thank you all for your responses. 
    I don’t know the air flow measurements, I know you can’t properly diagnose without them, it’s being fixed and I just don’t have it. Having said that, the filter is clean, the blower is clean, and all the supply and return vents are open and not blocked and nothing has changed in the house that would effect air flow. The split is 19 degrees, it’s 410A and changing the TXV was a mistake. 
    Thanks again. 
  • pecmsg
    pecmsg Member Posts: 3,690
    edited July 2021
    Your SH is fine because the x-valve is doing it’s job. 
    Low air flow. 
    What’s your Static pressures
  • mattmia2
    mattmia2 Member Posts: 7,329
    Bad capacitor or bad motor could change airflow along with people closing dampers...
    HVACNUT Member Posts: 4,938
    19° split? What's the problem?