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
THE MODULATOR VALVE
