Vogt
®
VT Service Manual 5-1
Electrical Controls
5. Electrical Controls
CONTROLS
Explanation.
The VT-Series ice machine is controlled by a PLC (Programmable Logic Controller). The
PLC controls the sequence of events and monitors the ice machine functions. The operational sequences of
the VT-Series ice machine can be described best as a series of six different modes. Each mode identifies
and defines a sequence of events that occur while in that mode and thereby cause it to move to the next
mode. Only one mode is active at a time.
Start-Up Mode.
The start-up mode is a function which prevents the premature automatic starting of the
machine at the time of installation, after a power interruption, or after a machine fault. During Start-up, the
machine will not start for two hours. This gives the crankcase heater time to boil any refrigerant out of the
compressor. The start-up mode may be bypassed at any time by pressing the “Manual Harvest” (Start)
button to immediately advance to the standby mode.
NOTE: While the machine is in the Start-Up Mode, the Fault Indicator light will remain “on” (will not be
blinking).
! CAUTION !
If the power has been turned off to the machine, make sure the compressor
crankcase is warm and there is no liquid refrigerant in with the oil before
restarting the unit.
! CAUTION !
Standby Mode.
The standby mode is a decision making mode. It monitors the position of all the various
switches in the control circuit and at the proper time decides which mode to advance to next.
Note: R404A machines are pumped down while in the Standby mode. If the pressure comes back up after
3 minutes, (the low pressure switch “closes”), the machine will go to the Pumpdown Mode.
Freeze Mode (Freeze Cycle).
The freeze mode is active during the normal ice making cycle. During
this time, liquid feed valve is energized (R404A machines only) and the circulating water pump and
compressor are running. The freeze time is determined by the PLC analog timer (0-3.5 min) plus 5 minutes.
(Minimum freeze cycle time = 5 minutes, maximum freeze cycle time = 8.5 minutes)
FIGURE 5-1
PLC – Programmable Logic Controllers
PLC: FX
1
s
PLC: FXos
Freeze cycle Timer (PLC analog pot)
Turn Clockwise to increase freeze time
Minimum Freeze Time = 5 min
Maximum Freeze Time = 8.5 min
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