1-5
The loaded cylinder bank will continue to operate
fully loaded until the solenoid valve control device is
energized and the gas bypass port is opened.
7
10
12
15
14
8
9
4
6
5
2
3
11
13
1
1. Solenoid Valve
2. Valve Stem
3. Gas Bypass Port
4. Spring Guide
5. Spring
6. Piston
7. Piston Bypass Valve
8. Bleed Orifice
9. Strainer
10. Suction Cavity
11. Cylinder Discharge
Valve
12. Valve Plate
13. Cylinder Suction
Valve
14. Discharge Piston
Check Valve
Assembly
15. Discharge Manifold
Figure 1-6. Compressor Cylinder Head Loaded ---
Hot Gas Bypass
1.5.2 SUCTION CUTOFF UNLOADER
The compressor is equipped with unloaders for
capacity control. This consists of a self-contained, suction
cut-off arrangement which is electronically controlled by
the temperature controller.
The capacity
controlled
cylinders
are easily
identified by the solenoid which extends from the side of
the cylinder head.
When the solenoid energizes,
cylinders unload, preventing suction gas from being
drawn into the cylinder (See Figure 1-7). The unloaded
cylinders operate with little or no pressure differential,
consuming very little power. A de-energized solenoid
reloads the cylinders as shown in Figure 1-8.
a. Major Working Parts
1. Solenoid and valve system
2. Unloader piston assembly
3. Spring and cover plate
b. Unloaded Operation
When the unloader valve solenoid energizes, the
capacity control valve port opens (item 3, Figure 1-7).
This allows the discharge gas behind the unloader piston
assembly (item 4) to vent back to the suction side. The
unloader valve spring (item 7) at this point, can move the
unloader valve body to the left, blocking the unloader
suction port. The cylinder bank is now isolated from the
compressor suction manifold to unload these two
cylinders. No refrigerant is allowed into the cylinders and
no compression takes place.
SUCTION PRESSURE
DISCHARGE PRESSURE
1
2
3
4
5
6
7 8
9
10
11
12
13
14
15
16
1. Solenoid Valve
2. Coil
3. Capacity Control
Valve (Open)
4. Unloader Piston
5. Cylinder Head
6. Valve Body
7. Valve Spring
8. Cover Plate
9. Suction Manifold
10. Suction Valve
11. Piston
12. Discharge Valve
13. Discharge Manifold
14. Valve Plate
15. Strainer
16. Bleed Orifice
Figure 1-7. Compressor Cylinder Head (Unloaded) ---
Suction Cutoff
c. Loaded Operation
When the unloader valve solenoid de-energizes, the
capacity control valve port closes (item 3, Figure 1-8).
This allows discharge pressure to build-up behind the
unloader piston assembly. The high pressure will
compress the unloader valve spring, opening the
unloader suction port. Suction gas can now be drawn into
the cylinders, running the bank fully loaded.
