CAPACITY CONTROL SYSTEM
The compressor capacity is controlled by the movement of
the inlet vanes, opening or closing to permit the correct quan-
tity of refrigerant to enter the wheel or impeller. The vane
movement occurs in response to oil flow from the SA or SB
solenoid valve which, in turn, respond to a control module
signal. This oil flow activates a piston to rotate the vanes.
VANE OPERATION
The hydraulic system for the vane control operation consists
of a
4-way normally open solenoid valve. Oil under pressure
is directed by the 4-way valve to either or both sides of the
piston depending on whether the control signal is to load,
unload or hold.
To open the vanes (or load the compressor) solenoid “SA”
is de-energized and solenoid “SB” is energized, allowing oil
flow from port SA to one side of the piston then drain through
port SB.
To close the vanes (unload compressor) valve SB is
de-
energized and valve SA is energized to move the piston and
vanes to unload position.
When both solenoid valves SA and SB are de-energized,
full oil pressure is directed to both sides of the piston through
ports SA and SB, thus the vanes are held in that position.
Refer to Figure 7 for solenoid action. Note that both solenoids
cannot be energized simultaneously.
METERING VALVES
The speed at which the capacity control vanes are opened
or closed can be adjusted to suit system operating re-
quirements. Adjustable needle valves in the oil drain lines
are used to control the rate of bleed-off and consequently the
“vane speed”. These needle valves are part of the
4-way
solenoid valve assembly located in the compressor lube box
(Figure 6).
The valves are normally factory set so the vanes will move
from fully closed to fully open in approximately 3 minutes and
from fully open to fully closed in 1 minute (except CE126).
The speed should be slow enough to prevent over-controlling
and hunting. For adjustment procedure, refer to the Ad-
justments section of this manual
FIGURE 6. LUBE BOX
Vane Closed
Switch
)/
,
-0penlng
---+
-Closing
4.Way
Solenoi
Valve
I
Oil Pressure
Differential
-
Switch
IGURE
7. VANE CONTROL SOLENOID OPERATION
-LEGEND-
- Oil Under Pressure
I
Oil Sump Pressure
COMPRESSOR
UNLOADER
CYLINDER
FLOATING
PISTON
LlNKED
TO
INLET
VANES
---p
OPENS VANES
L
CLOSES
VANES
FOUR
WAY
SOLENOID
VALVE
LOCATED IN
LUBE BOX
TO
OIL
+
PUMP
SUMP
SECTION “SB”
DE-ENERGIZED
ADJUSTABLE
NEEDLE VALVES
INTEGRAL
WITH
FOUR WAY
SOLENOID
VAL
VE
FROM OIL
PUMP
DISCHARGE
Page 10
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IM 307
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