Vogt VT100, Service Manual

Page: 31 / 76

5-2 Vogt
®
VT Service Manual
Electrical Controls
Harvest Mode (Thaw Cycle).
The harvest mode is normally initiated at the termination of the freeze
mode. At this time, the circulating water pump stops and the liquid feed valve closes (R404A machines
only). After five seconds, the “D” (thaw gas) solenoid valves open and the chopper motor starts. On split
VT40’s & VT60’s, the hot gas loop valve energizes and VT80 & VT100 the suction stop valve energizes
when the chopper starts and thaw gas valves open. When the suction pressure reaches the set point on the
Harvest Hold (HH) pressure switch (PLC input #2 light will turn “off”), the harvest timer will begin to time.
The harvest timer is an internal timer in the PLC set for 45 seconds.
The harvest mode is terminated by the PLC thaw (harvest) timer at which time the machine will begin
another freeze cycle. The harvest mode can also be terminated manually by pushing in the “Manual Harvest
(Start)” button.
Increasing Harvest Time – To increase the harvest cycle time, raise the HH pressure switch cut-out setting.
(See Figure 5-2) This will increase the time it takes for the suction pressure to reach the set-point on the
switch, thereby increasing the harvest time.
FIGURE 5-2
Harvest Hold Pressure Switch
(located on top of lowside control panel)
Long Harvest Cycle Safety – The PLC monitors harvest cycle time. If the suction pressure does not reach
the HH pressure switch set-point within
3 minutes , the machine will shut down and go to the Fault Mode.
NOTE: If the “Selector Switch” switch is in the “Off” position or the bin control is satisfied the machine will
complete the Freeze, Harvest and Pumpdown cycle before shutting off (standby mode). Machines with R22
do not go through a pumpdown cycle before shutting off.
Pumpdown Mode
(R404A machines only)
.
All R404A machines have a liquid feed solenoid valve and
go through a Pumpdown cycle before shutting off. During the Pumpdown cycle the water pump and
compressor are “on” and the liquid feed solenoid valve is “closed”. The machine will run in the Pumpdown
mode until the Low pressure safety switch “opens”. After shutting off on low pressure, the machine will go to
the Standby mode.
Note: If the suction pressure does not reach the cut-out point on the low pressure switch within 2 minutes,
the machine will fault out on a “Pumpdown Fault”.
Continuous Pumpdown
(R404A machines only). While in the Standby mode, the machine will
remain pumped down. After a 3 minute delay, if the pressure comes up in the freezer and the low pressure
safety switch “closes” (pressure gets above 20 psig), the compressor will come “on” and pump the machine
down.
Cut-In Setting
Clockwise – Lowers setting
set @ 45 psi (R22)
set @ 60 psi (R404A)
Cut-out Setting
Clockwise – Raises setting
set @ 65 psi (R22)
set @ 80 psi (R404A)