McQuay RAH 047C Installation And Maintenance Manual page 113

Phase Voltage Monitor (PVM)
The phase voltage monitor
three-phase loads from damaging power conditions. A
microprocessor-based voltage and phase sensing circuit
constantly monitors the three-phase voltages to detect harmful
power line conditions. When a harmful condition is detected,
its output relay is deactivated after a specified trip delay (Trip
Delay). The output relay reactivates after power line
conditions return to an acceptable level for a specified amount
of time (Restart Delay). The trip and restart delays prevent
nuisance tripping due to rapidly fluctuating power line
conditions.
Figure 128: Phase Voltage Monitor
Standard
2%–8%
variable
voltage
unbalance
There are two LEDs on the face of the PVM ("1" in
Figure 128) to indicate the following:
Table 27: LED Indication
Status
Normal operation, no faults,
relay energized
Loss of input phase (relay de-
energized)
Voltage unbalance (relay de-
energized)
High or low voltage (relay
de-energized)
Phase reversal (relay de-
energized)
Restart delay (fault cleared,
PVM pending restart, relay
de-energized)
McQuay IM 987
(Figure 128) is designed to protect
Standard
1–500 second
variable
restart delay
Standard
1–30 second
trip delay
4
LED display
1
LED Indicator
Green LED - steady on
Red LED - flash twice, off,
flash twice, off, etc.
Red LED - flash twice, off,
flash twice, off, etc.
Red LED - steady on
Red LED - pulse on, off, on,
off, etc.
Green LED - pulse on, off,
on, off, etc.
Other features:
• Standard 2% to 8% variable voltage unbalance ("3" in
Figure 128).
• Standard 1 to 500 second variable restart delay ("2" in
Figure 128).
• Standard 1 to 30 second trip delay ("4" in
(except loss of phase, which trips at 1 second non-
adjustable).
Disconnect
Hazardous voltage. Will cause severe injury or death.
Disconnect electric power before servicing equipment. More
than one disconnect may be required to de-energize the unit.
The optional disconnect is a "through-the-door" molded case
switch with similar features of the circuit breaker. The
"through-the-door" feature provides a safety interlock that
disables power when an inexperienced person opens the
control panel door. This is not the normal recommended
method to access the control panel or to disable power to
an operating unit.
Molded case switches do not provide over-current protection.
This device may automatically open the circuit at levels above
the ampere rating of the switch.
Depending on the desired operating state of the unit, four
different recommended methods can be utilized to access the
control panel or to disable power.
Recommended method to access the controls through the
1
"release" method (defeats the mechanical interlock and
allows the control panel door to open without
disconnecting power - switch is in the power "On"
position):
Obtain a small standard head screwdriver.
a
Insert the head of the screwdriver into the slotted
b
"release" located on the right hand side of the
disconnect faceplate
counter-clockwise.
Pull open the door after the mechanical interlock is
c
released.
Recommended normal method to turn off an operating
2
unit (no emergency condition present):
Follow the "release" method described above.
a
Use the pump down switch to turn off the unit.
b
The controls will then shut the liquid line solenoids,
c
pump the refrigerant into the condenser, and turn off
the compressors.
Maintenance
Figure 128)
DANGER
CAUTION
(Figure 129). Turn the release
113