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will allow one automatic retry (after soft lockout delay)
before disabling the compressor in a hard lockout
(requires manual reset). If hard lockout does occur,
the ALR terminal on the CCM will become active with
24v, which will power the high pressure relay within
the wall unit. The relay contacts are monitored by the
unit controller. If the CCM indicates an alarm to the
wall unit controller, an alarm will be generated and the
compressor will be locked out by the controller.
NOTE:
The controller will remove cooling call on the Y
terminal of the CCM, reseting it almost instantly.
The compressor remains locked out by the
controller until manually cleared.
Switch is jumpered in this application. Instead, the low
pressure transducer is used for low pressure monitoring.
High Pressure Safety Switch
All units have a high pressure switch as a safety device.
This device will open when pressure in the system
reaches 650 PSIG. The sensor is directly connected to
the dedicated compressor control module. This module
will disable any call for cooling if the pressure is above
this limit. If tripped, the high pressure switch can be
reset by turning the output off and then back on again.
Phase Monitor
Used only on three phase equipment, the phase
monitor is a compressor protection device that will
prohibit operation of the compressor if the device senses
a possible reverse-rotation situation due to incorrect
phasing. On a call for compressor (and only compressor),
the device will check incoming phase, check for severe
voltage imbalance and check for proper frequency.
Under nominal conditions, a green LED light will show
on the face of the monitor. If there is improper phasing,
voltage imbalance or frequency deviation, the device will
show a red LED light and prohibit compressor operation.
If a fault condition occurs, reverse two of the supply
leads to the unit.
Do not reverse any of the unit factory
wires as damage may occur.
Compressor Operation
The compressor will be enabled when the unit (in stand
alone mode) or LV provide a cooling stage 1 call. The
compressor call from the controller has several delays
that may affect the start or stop time of the compressor
in regards to the cooling demand. The compressor has
a minimum on time of 120 seconds to prevent short
cycling the compressor. The compressor also has a
minimum off time of 120 seconds to prevent start
ups before the pressure in the refrigeration system
equalizes. When the second stage is engaged, it also
has a minimum run time of 120 seconds to allow the
system to stabilize before returning to single stage or
shutting down.
These delays can be changed by:
1. Press MENU key to go to the Main Menu screen.
2. Press UP or DOWN keys and ENTER key to enter
USER password 2000.
3. Press UP or DOWN keys to scroll to
Adv System
Config
; press ENTER key.
4. Press UP or DOWN keys to scroll to
Unit Config
(B2)
; press ENTER key.
5. Press ENTER key to scroll to
Min On
,
Min Off
,
Min On Same
,
Unloader Del or Address Delay
(see
Figure 2.27).
6. Press UP or DOWN keys to change the value.
7. Press ENTER key to save value and move the
cursor to next parameter or top of screen.
8. Press ESCAPE key several times to return to Main
Menu screen.
The address-based delay only applies to the wall unit
when in stand alone mode. The controller will delay the
unit compressor based on the value entered on screen
B2 multiplied by the unit address. This is intended to
keep multiple units from starting their compressors
at the same time when there is a quick change in the
load. When connected to the LV, this is taken care of by
LV logic.
FIGURE 2.27
Adjusting Compressor Delays
Compressor Alarms
Refrigerant High Pressure Alarm
When the wall unit receives a signal from the
compressor control module (CCM) indicating a high
pressure event, the wall unit will generate an alarm.
Upon receiving the alarm, the wall unit will remove
the “Y” call from the CCM, resetting the status of the
CCM. The alarm will stay present on the wall unit until
manually cleared.
In addition to the CCM, the discharge pressure
transducer is used to prevent a high pressure event.
When the discharge pressure is above the discharge
pressure alarm setpoint (set 30 pounds below high
pressure switch, which is 650), the system will disable
stage 2 of mechanical cooling.
