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air balance issue

I was working on a packaged united cool air unit model# va5g3as serial# 041103. It is basically a giant through the wall unit,5 ton capacity, 1 hp supply fan motor.The issue is the unit is low on airflow, and based on what I can come up with it has been that way since it was built.The filters are clean, the coil is clean, and based on a duct traverse reading that I took the unit is moving 1500 cfm.Far short of the 2000 cfm that I would expect.The motor sheave is all the way in, and the brake hp calculated on the supply fan is 1.05 hp. Short of upgrading the motor to a larger hp,which I don't want to do fearing that It will destroy the blower,I don't know what to do other then suggesting changing the unit out or adding a supplemental unit.I took a sensible airflow calculation across the electric heater, and it was within 200 cfm of the traverse reading.To me the unit is maxed out, and incapable of moving any more air. Any suggestions would be much appreciated thanks to all.


  • Spence
    Spence Member Posts: 316
    Any unit will only move air in relation to the blower's ability to overcome any component pressure drops and the resistance of the duct system.
  • Matt_67
    Matt_67 Member Posts: 193
    Is the motor drawing higher than RLA? What kind of filters are in the unit?
  • Techman
    Techman Member Posts: 2,144
    edited July 2015
    Can you see both sides of coil? What kind of S/R ducts?. Possibly your allowed(Mfrg) to increase the driven pully and play w/ the drive pully?

    A bigger hp motor will still be at the same RPM.What is motor amps vs nameplate amps? Volts in bldg/unit and freon P/T , because you should be having freon related problems also
  • Empire_2
    Empire_2 Member Posts: 2,343
    Through the wall? As in P-Tak? 5 ton? am I correct in you mod#? Are you sure it's not 3 ton? Just asking....

    Mike T.
  • zepfan
    zepfan Member Posts: 309
    yes five ton, three phase
  • Lance
    Lance Member Posts: 142
    Static pressures need to be checked. Whose to say what you see is supposed to be there? Pulley size even the fan belt size, type can make a difference. Many a wrong substitute belt has been installed. If all things are correct is the gap between the blower and the housing centered and proper? A squirrel cage fan can loose air flow when this is not properly positioned. Also in duct work especially in the larger tonnages elbows too close to blowers and too many of them can reduce air flow. Trust nothing suspect everything. Rotation? Voltage? Run capacitor if involved? Just some thoughts to consider?
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