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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

Comments

  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,047Member
    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
  • JUGHNEJUGHNE Posts: 6,045Member
    I learned on my first 410A job how easy it is to overcharge those, especially if microcoil.
  • JUGHNEJUGHNE Posts: 6,045Member
    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??
  • ChrisJChrisJ Posts: 10,143Member
    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
  • JUGHNEJUGHNE Posts: 6,045Member
    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.
  • unclejohnunclejohn Posts: 1,420Member
    Heat pump or straight A/C? Mod # please,
  • Steve MinnichSteve Minnich Posts: 2,468Member
    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.
    PHC News Columnist
    Minnich Hydronic System Design & Consultants
  • hvacfreak2hvacfreak2 Posts: 474Member
    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 ).
    hvacfreak

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

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