AADCO 737 Series, Operating Instructions Manual

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36
14.0 PRESSURE SWITCH ADJUSTMENT
14.1
The pressure switch, Figures 5, 6 and 11 (17), controls the pressure range for
compressor operation. This range is usually between 60 and 80-psig.
14.2
The two opposing but adjacent white, knurled knobs (one considerably larger
than the other) are accessible without removing the dark plastic cover. These
knobs determine upper and lower range settings. They are interactive
adjustments; i.e., varying one will influence the setting of the other but not to a
great degree. The larger knob controls the upper pressure setting and is
continuously variable through ten to twelve full turns. The smaller knob is
variable only through 270

rotation.
14.3
The INPUT PRESSURE gauge is the operator’s pressure reference for the
adjustment procedure.
14.4
With the PUMP switch off and all pressure drained from the system by allowing
the POWER switch to remain on, adjust the smaller, white knob on the
pressure switch about midway of its travel. This is an arbitrary setting and later
will be further adjusted.
14.5
Depress the PUMP switch on and POWER switch off and observe that
pressure on the INPUT PRESSURE gauge at which the compressor cuts off.
This should be about 80-psig. If not at 80-psig but at some lower pressure,
rotate the larger knob clockwise so that the black ring on the knob moves to a
higher pressure setting, as observed on the pressure scale of the switch
(calibration marks 0-260 psig) and vice versa if too high.
14.6
Depress the POWER on switch so that air is bled from the ballast tank by the
system and the input pressure will decrease. Make a note of that pressure at
which the compressor cuts on. This should be about 60-psig.
14.7
If the observed pressure in Section 14.5 were not 80-psig but some higher
pressure, rotate the larger knob so that the black ring on the knob moves
toward a lower pressure reading on the switch pressure scale. As the input
pressure increases, once again note that pressure at which the compressor
cuts off. From the incremental decrease from the initial pressure reading and
the amount that the larger knob was turned, a determination can be made as to
how much, approximately, is required to make that setting for compressor cut
off at 80-psig.
14.8
After completing the setting which controls the 80-psig compressor cut off,
observe the 60-psig reading. If too low, turn the small, white, knurled knob
clockwise to increase its reading and counter-clockwise to decrease its setting.
After each adjustment of the small, white, knurled knob, the larger knob must