Taylor-Wharton CS Series - Manual (Page 38)

36
CS SERIES
Removing/Installing the Solenoid Valve
The LN
2
and power must be turned off before beginning work on the solenoid valve.
For LABS Units
Disconnect only the solenoid valve lead connection from the back of controller
board.
To remove the solenoid valve, loosen the compression fitting that connects the
plumbing tubing to fill tube. Unscrew the two (2) mounting screws that hold the
solenoid valve to the solenoid bracket. Then remove the solenoid valve and its
associated plumbing. Disconnect the plumbing from the inlet and outlet side of the
solenoid valve.
To install a new solenoid valve, attach the connecting plumbing to the inlet and
outlet connections of the valve using Teflon tape on tapered threads (3 wraps).
Attach the compression fitting to the fill tube first and then connect the compression
fitting to the elbow that is connected to the outlet side of the solenoid valve. Position
the solenoid valve onto the solenoid valve bracket and tighten the two (2) mounting
screws. Attach the solenoid valve lead connection to the controller board.
Controller Electrical Tests
If a controller is removed from the refrigerator for service, the liquid refrigerant
level must be maintained manually to protect stored product. The fill solenoid valve
will be inoperative with the controller removed. A flexible fill line terminated with
a phase separator may be used periodically through the open refrigerator lid to
conduct manual fill operations until automatic operation is restored.
Sensor Probes. The sensor probes used to detect liquid level by Taylor-Wharton
controllers are temperature-sensitive resistors called “thermistors.” Their resistance
to electrical current flow changes greatly with their temperature.
• At Room Temperature ....2 ohms to 10 ohms
• In Cold Nitrogen Gas ....8 K ohms to 18 K ohms
• In Liquid Nitrogen .........18 K ohms to 35 K ohms
Controller Logic. The liquid level controllers read the values of the sensors as
indications of liquid level. The function of a sensor, and its value, are interpreted by
the controller to set normal operating, fill, fill termination, and alarm conditions. In
addition, the refrigerator temperature is monitored and an alarm is triggered if the
temperature raises above a pre-determined point.
• From cold gas to liquid ..Resistance greater than 22K ohms.
• From liquid to cold gas ..Resistance less than 16K ohms.
• Defective Sensor ............Resistance greater than 50K ohms, or less that 5 ohms.