Vogt TUBE-ICE 05TA, Service Manual

Page: 77 / 111

05TA Service Manual
SERVICE OPERATIONS
8/13/01
9-13
Capacity Control (Internal) Valve Construction. A schematic illustration of the internal valve
operation is shown in FIGURE 9-7.
In the normal (full capacity) operating position with the solenoid valve de-energized, the needle valve
is seated on the lower port, and the unloading plunger chamber is exposed to suction pressure
through the suction port. Since the face of the plunger is open to the suction chamber, the gas
pressures across the plunger are equalized, and the plunger is held in the open position by the spring.
When the solenoid valve is energized, the needle valve is seated on the upper port, and the unloading
plunger chamber is exposed to discharge pressure through the discharge pressure port. The
differential between discharge and suction pressure forces the plunger down, sealing the suction port
in the valve plate, thus preventing the entrance of suction vapor into the unloaded cylinders.
The seal on the unloading plunger minimizes any leakage in pressure so that a pumpdown cycle may
be used with the valve either energized or de-energized without excessive compressor cycling.
FIGURE 9-7
Loaded Operation (during freeze).
This capacity control valve is controlled by an electric solenoid.
When the solenoid is de-energized, the valve loads the cylinder bank (2 cylinders) as shown in the
above figure.
Unloaded Operation (during thaw only). During the thaw cycle, the solenoid coil is energized.
The needle valve is seated on the upper port, and the unloading plunger chamber is exposed to
discharge pressure through the discharge pressure port. The differential between discharge and
suction pressure forces the plunger down, sealing the suction port in the valve plate, thus preventing
the entrance of suction vapor into the unloaded cylinders.