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MAINTENANCE
Crusader
MC...;8
[ e.c, _ _
16_-_31 _ _ DAIE__;:;__Ja--'-nu_ary,._,_,_19_75_]
MANUAL
FILTER-DRYER
A filter dryer is installed between the receiver
tank and expansion valve. It is used to absorb
moisture from the refrigerant. The filter should be
replaced if the system has been open to prolonged ex-
posure as shown by the moisture indicator sight glass.
When the moisture indicator sight glass indicates a
blue color then the system is "dry" (normal) con-
d\tion. Wh_en the moisture indicator sight glass in-
dicates a pink color then the system is "Wet" or has
moisture in the system, then the filter dryer should be
replaced.
A plugged dehydrator is indicated by differences in
temperatures gn either side of the dehydrator.
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Figure
16-45A:
Filter Dryer
REPLACEMENT
Pump
down
the
system
by
isolating
the
refrigerant in the receiver and reducing pressure at
the dryer.
I) Install a service gauge at the compressor.
2) Close off the outlet from the receiver tank.
3) Run the compressor until the low side of the
system is evacuated.
4) Change dehydrator element.
5)
Admit a small quantity of Freon to the low side
of the system. Check for leaks. Return the system
to normal operation.
CAUTION: Do not use carbon tetrachloride or
similar solvent to clean parts. DO NOT use steam
guns. Use mineral spirits, white gasoline or naphtha.
All parts should be thoroughly cleaned. Use a stiff
brush to wash dirt from grooves, holes, etc.
EXPANSION VALVE
DESCRIPTION
The expansion valve is a thermo-sensitive valve with
a remote control bulb head attached to the evaporator out-
let line. The valve regulates the flow of liquid refrigerant
into the evaporator coils and is controlled by the sucti-on
gas temperature leaving the evaporator.
One expansion valve may be used rn the main eva-
porator for Freon 12 and one expansion valve for Freon
500, also one expansion valve may be used in the driver's
evaporator for Freon 12 and one expansion valve for Freon
500.
The bulb head senses the gas refrigerant temperature as
it leaves the evaporator. High temperature will cause ex-
pansion and pressure on the power head and spring. Such
action causes the power assembly valw to open. allowing
a flow of liquid refrigerant into the naporator.
OPERATION
The remote bulb and power assembly 1s a closed sys-
tem. The pressure within the remote bulb and power
assembly then corresponds to the saturation pressure
of the refrigerant temperature leaving the e\aporator
and moves the valve pin in the opening dm:ct1on. Op-
posed to this force on the underneath ,1de
of
the dia-
phragm and acting in the closing direction. is the force
exerted by the evaporator pressure. and the pressure ex-
erted by the superheat spring. As the tcmrerature of
the refrigerant gas at the evaporator ,>utlct increases
above the saturation temperature corre~ponding to the
cvarorator pressure. it becomes superheated. The pre-
ssure thus generated in the remote bulb and power as-
sembly increases above the combined rressures of the
evaporator pressure and the superheat spring. causing
the valve rin to move in the opening direction. Con-
versely as the temperature of the refrigerant gas leaving
the evaporator decreases, the pressure in the remote
bulb and power assembly also decreases and the com-
bined evaporator and spring pressures cause the valve
pin to move in the closing position
As the operating superheat is raised. the evaporator
capacity decreases. since more of the evaporator surface
is required to produce the superheat necessary to
open the valve. It is obvious, then, that it is most im-
portant to adjust the orerating superheat correctly and
that a minimum change in superheat required to
move the valve rin to full open position. 1s of vital im-
portance because it provides savings in both initial ev-
aporator costs and cost of operation. Accurate and sen-
sitive control of the liquid refrigerant flow to the ev-
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