McQuay IM 987
113
Maintenance
Phase Voltage Monitor (PVM)
The phase voltage monitor (
Figure 128
) is designed to protect
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
There are two LEDs on the face of the PVM (“1” in
Figure 128
) to indicate the following:
Table 27: LED Indication
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
Figure 128
)
(except loss of phase, which trips at 1 second non-
adjustable).
Disconnect
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.
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.
1
Recommended method to access the controls through the
“release” method (defeats the mechanical interlock and
allows the control panel door to open without
disconnecting power - switch is in the power “On”
position):
a
Obtain a small standard head screwdriver.
b
Insert the head of the screwdriver into the slotted
“release” located on the right hand side of the
disconnect faceplate (
Figure 129
). Turn the release
counter-clockwise.
c
Pull open the door after the mechanical interlock is
released.
2
Recommended normal method to turn off an operating
unit (no emergency condition present):
a
Follow the “release” method described above.
b
Use the pump down switch to turn off the unit.
c
The controls will then shut the liquid line solenoids,
pump the refrigerant into the condenser, and turn off
the compressors.
Status
LED Indicator
Normal operation, no faults,
relay energized
Green LED - steady on
Loss of input phase (relay de-
energized)
Red LED - flash twice, off,
flash twice, off, etc.
Voltage unbalance (relay de-
energized)
Red LED - flash twice, off,
flash twice, off, etc.
High or low voltage (relay
de-energized)
Red LED - steady on
Phase reversal (relay de-
energized)
Red LED - pulse on, off, on,
off, etc.
Restart delay (fault cleared,
PVM pending restart, relay
de-energized)
Green LED - pulse on, off,
on, off, etc.
1
Standard
1–500 second
variable
restart delay
LED display
4
Standard
1–30 second
trip delay
Standard
2%–8%
variable
voltage
unbalance
DANGER
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.
CAUTION
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.
