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Fig. 8. Modulator Valve and By-Pass System
Equally important is the capping of lines or openings
into any of the units in the existing system that are
exposed while repairs are being made.
The refrigeration system as it has been described
would operate satisfactorily providing the compressor
was driven at a constant speed. In order to
compensate for the variable speed operation of the
engine driven compressor in our Lincoln air
conditioning system, it is necessary to place an
automatic device in the sys-tem to control the
compressor pressure. This device is called a
modulator valve.
Because of the moisture problem, factory
replacement parts, including all tubing, have been
thoroughly dried and all openings capped. These
replacement parts must be installed as rapidly as
possible after the caps are removed.
The modulator valve is so designed that
compressed vapor can be by-passed to the intake
side of the compressor to maintain a uniform inlet
or "low pressure side" pressure. Thus as the
compressor speed increases, and the pressure on
the low pressure side drops, vapor pressure is
returned to the low pressure line to raise the
pressure in the line. See figure 8.
The modulator valve can also be manually controlled
to regulate the low pres-sure in the system. If the low
pressure is lowered, there will be greater refrigerating
action in the evaporator. This is the action that takes
place when the manual control lever at the instrument
panel is moved to the "cooler" position. See figure 9.
An inoperative modulator valve, like an inoperative
expansion valve, can also cause a serious malfunction
in the system. For example, if the automatic feature of
the modulator valve should
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