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Home AC Compressor High-Side Pressure Cycling

My 7 yr old 2.5 ton Goodman AC unit is now working OK (the thermostat failed!), but the svc tech noted that the high-side pressure slowly cycles from 380--580 psi (~every 10 seconds), and the amp draw there is in synch with that at 8.5--12 amps. Any idea what to look for???? It DOES work, but that pressure over the nominal 450psi is troubling. --gdb


    EBEBRATT-Ed Member Posts: 15,526
    If the condenser fan is running normally then the condenser coil probably needs cleaning. Spray coil cleaner on it and flush with water. Follow the directions on the coil cleaner and folly good safety practices. Power off, rubber gloves face protection.

    About the only other reason would be if the unit was overcharged
    JUGHNE Member Posts: 11,061
    I learned on my first 410A job how easy it is to overcharge those, especially if microcoil.
    JUGHNE Member Posts: 11,061
    Ed, I can see how the pressure would be up from plugged coil or overcharge......but how does it drop and then rise again?
    (assuming the unit stays running)
    Could be TXV searching??
  • ChrisJ
    ChrisJ Member Posts: 15,686
    edited May 2018
    Normal 450? 450 even sounds excessive

    Non condensibles, txv probe in wrong spot, oversized txv, overcharge will cause such issues.

    What model units both indoor and outdoor? Txv or piston?

    What was the suction side doing? What's the superheat and subcooling?
    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
    JUGHNE Member Posts: 11,061
    Has anyone checked the pressures since the original install?
    Could this have been going on since day one?
    I see ChrisJ's point on the non condensibles (air) in there that may run the pressure up and down.

    The tech should have noticed the plugged coil if so.
  • unclejohn
    unclejohn Member Posts: 1,833
    Heat pump or straight A/C? Mod # please,
  • Tinman
    Tinman Member Posts: 2,808
    Non-condensable gases, overcharge, restriction depending on what suction pressure is doing, underperforming fan (1 or 2 speed?), dirty coil (some coils are two layered), air obstruction surrounding the unit.
    Steve Minnich
  • hvacfreak2
    hvacfreak2 Member Posts: 500
    I'm going with failed expansion valve after reading the symptoms in the OP. I got volunteered for a favor on one of these and saw the exact same as described. The good news is that if you go back with an OEM valve the connections are all mechanical ( Rotolock type from memory ).

    Mechanical Enthusiast

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