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Does or can an excessive suction like cause a pressure droip?

<strong>Correct mi F I'm wrong, but can the excessive suction line cause a pressure drop.  I was on a job and measures the LL and SL.  Both were in excess of 110 foot.  Head seemed to be normal but the suction pressure maintained at about 52 psig with a S/H of 23*.....  Condenser is on ground floor and A/H on the second floor set back a way.</strong>   A Coil is spotless and absolutly no traps amywhere to be found.


<strong>Mike T.</strong>


  • Tom Blackwell_2
    Tom Blackwell_2 Member Posts: 126

    A short answer is yes, but the real issue is the liquid line lift. For the refrigerant to remain a liquid before it gets to the evaporator coil requires enough subcooling of the liquid to accomplish the lift to the coil location plus an additional amount for the liqiud line pressure drop. You'll probably have to add additional refrigerant to increase the subcooling to the point that the metering device can flow enough refrigerant to satisfy the coil conditions. If the pressures are still suspect, then add a schraeder valve at the coil outlet and compare suction readings. Suction line pressure loss should not be over 10 psi for a normal air conditioning application.
  • Techman
    Techman Member Posts: 2,144
    edited August 2010
    Think TXV

    Empire,HOW RU ,MIKE!!!!!!!The press drop thru an evap coil determines wheather an internally equilized or and externally equilized TXV is used.Press drop= temp drop,also.What size line set and tonnage of system? Inverter technoligy?I agree w/ Tom,put  in an acess fitting at the A.H.U. Is the suction press gauge accurate.? I misdiagnosed a few  this summer 'cause of that. I think 10 psig press loss is from the metering device outlet ,evap coil,and suction line to the comp inlet .I think 10 psig loss just for the suction line is a lot.A suction filter/drier r-22 is only allowed 2-3 psig drop and it has to be removed/replaced.
  • Eugene Silberstein_2
    Eugene Silberstein_2 Member Posts: 349
    Be careful where you calculate superheat

    Greetings Mike...

    Idealy, we calculate evaporator superheat at the outlet of the evaporator. Given the long run of the suction line, you will definitely experience a lower than desired suction pressure and a high evaporator superheat. To get a more accurate superheat value, without having to install a service port at the evaporator, simply take a suction line temperature reading at the outlet of the evaporator and compare it to the suction line temperature at the condensing unit. Take this difference and subtract it from your present superheat value.

    Hope all is well with you!
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