Taylor-Wharton 24K w/ AutoTend - Manual (Page 39)

LIQUID. NOTE THAT THE low level alarm ceases, fill solenoid valve is still open.
Control is flashing FILLING.
•
Manually press STOP button and note that the fill solenoid valve closes.
• Press FILL button to re-open fill solenoid valve.
• Continue to lower the sensor until the STOP FILL thermistor is immersed in the
LN
2
. Thefill should stop after a confirming (CHECK) SPLASH GUARD period.
•
Simulate an over fill by lowering the next thermistor into the LN
2
. HIGH LEVEL
alarm should sound with 10 seconds.
•
Re-install sensor assembly and thermocouple into sensor tube as before. Open
supply valve on LN
2
supply.
Indicates Low LN
2
Supply
When the START FILL thermistor is uncovered, the controller calls for the fill solenoid
valve to open. If the STOP FILL thermistor is not covered with LN
2
in the pre-deter-
mined amount of time, the controller is programmed to interpret this as a LN
2
supply
shortage.
1. Check contents gauge and pressure gauge of supply cylinder. Both liquid con-
tents and pressure (15 to 22 psi) are required to complete a fill.
2. Confirm that no other transfer hose or apparatus is attached to the supply cylin-
der. Either could compromise adequate tank pressure required to complete a fill
in 30 minutes.
•
Check the distance that the LN
2
must travel to reach the freezer. Observe the
time it takes for Liquid LN
2
to reach the Freezer through the usual piping condi-
tions (Pipe-Temperature at start fill). Liquid should be entering the chamber within
4 minutes under normal (usual) line temperature conditions.
•
Distances over 6 feet without a gas by-pass are discouraged due to excessive
boil off. Un-insulated fill line for the last 4 feet are encouraged to drive down
vapor temperatures in the freezing chamber during each fill.
•
A “Keep-Cold” or a “Keep-Full” device are almost always needed on an LN
2
pipeline, whether the pipe is Vacuum Jacketed or Foam Insulated.
3. Confirm that the solenoid valve is open when a fill is called for.
•
If no flow is detected, the solenoid valve is not getting the signal to open, or it is
opening and there is a blockage in the line. Check the connections on the leads
near the solenoid itself, as well as the connector at the controller.
•
Confirm that the wires have not been pinched, creating a short circuit. The joint at
the cabinet top to cabinet side is often the pinch point from previous service calls.
4. If a longer fill time is desired, change the setting by selecting: MENU, SYSTEM
ALARMS, LN
2
SUPPLY ALARM.
Indicates Open Sensor
1.
Normally, this message is associated with a loose plug or connector. Check the
connection at the foot of the controller labeled SENSORS.
2. If the problem persists, the sensor assembly may need to be replaced. To
determine this select: MENU, LEVEL SENSING, TEST LEVEL SENSORS. An
“L”, “G”, or “O” (open) will indicate individual thermistor status. If you still suspect
the controller, confirm the sensor integrity using an ohm meter. Refer to Figurer
15 Pin View Schematics.
•
Thermocouple is not repairable. Replace from stock.