To establish the pressure drop, pump the system down and fit a service gauge to the 1/4” flare connection on the distributor
cap. Restart the system. The dierence between the pressure at at the distributor and the suction pressure is eectively the
‘pressure drop’ . Using the graph below plot the pressure drop value on the requisite curve. The solid portion of the curve
represents the operating band of the device.
If the value falls outside this band, plot downwards from this point to determine the ratio. Multiply the diameter of fitted orifice
by this ratio and the resultant is the diameter of the orifice required. If the larger of the two orifices is oversize, drill out the
smaller orifice to suit. Always drill undersize then recheck the pressure drop to determine whether further enlargement is
necessary. If the pressure drop is within upper limits of the curve (solid portion) but the TEV is unstable, the orifice must be
further enlarged to bring the pressure drop closer to the normal operating point.
Note
An extreme measure can be to discard the orifice assembly entirely. If the problem still persists, it is possible that the TEV is
either faulty, undersized or lacks sucient refrigerant liquid subcooling. These faults must be corrected before adjustments
can be made to the distributor system.
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