Fridgewatch 2000 Controller Mk5
Publication 3-59 Section 3
Page 71 of 222 Issue 3.2 : 05.23
15.7.2. Current Limiting
Current limiting, the type of limiting input most commonly used, protects
the compressor motor and VSD or switch gear from damage which may
occur if the motor tries to exceed the design full load current.
Motor current is displayed as monitoring point P5.
When current limiting is implemented, Fridgewatch senses motor current:
Via a 1 V ac analogue input from a 1 amp current
transformer terminals 155/156, sensing current in the line
conductor
or
By a 4 to 20 mA signal from a motor current transmitter
terminals 155A/156A.
If the measured motor current exceeds S65, Fridgewatch inhibits load
pulses from the control algorithm, preventing the compressor from
loading.
Event codes E21 - Limiting - Info Only and E85 - Compressor Motor
Current (P5) High - Load Inhibit are shown when current limiting is taking
place.
If, however, the motor current continues to increase and the second,
higher, S66 value the Fridgewatch unloads the compressor until the
measured current falls below the higher value.
Event codes E21 - Limiting - Info Only, E85 - Compressor Motor Current
(P5) High - Load Inhibit and E96 - Motor Current (P5) High - Force
Unload are shown.
15.8. Pump-down
Pump-down is implemented by linking or closing contacts across
terminals 217/218; refer to Fig 56.
Pump-down can be terminated by contacts of a mechanical pressure
switch connected across terminals 217/218 breaking when suction
pressure falls to the required value.
Alternatively, Fridgewatch can be configured to terminate pump-down
when the measured value of P2 or P11 falls to the required value.
S172 is the termination pressure value for P2.
S173 is the termination pressure value for P11.
The pump-down process never lasts longer than 180 seconds as an
override timer terminates pump-down if, for any reason, the mechanical
contacts fail to open, or the pressure fails to fall to the termination value.
NOTE: If pump-down is NOT used, DO NOT link 217/218.
If pump-down is implemented, it is always applied during stopping.
Pump-down can additionally be applied to starting by setting S171 to 173.
With pump-down on stopping implemented, the liquid line solenoid valve
connected across terminals 284/285 is de-energised (closed) when the
compressor is required to stop.
The compressor continues to run, pumping over charge from the
evaporator into the condenser and liquid receiver, until the pump-down
pressure switch contacts open, the termination pressure value (S172 or
S173) is reached or the override timer expires after 180 seconds (fixed
duration).
Pump-down on starting operates in a similar way, although this time the
liquid line solenoid remains de-energised (closed) when the compressor
starts until the terminate pump-down condition is true.
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