McQuay PE046W Installation Manual
USED ON ALL PE, PH. PJ, PG
TPE, TPF, TPH, TPJ MODELS
THROUGH DECEMBER
31,1982
USED ON ALL
AND PF UNITS SINGLE AND DUAL
MODELS THROUGH DECEMBER
PE046W-06OW
31,1982
GENERAL
Prior to January 1, 1982 a number of different control
panels were utilized on the model PE and PF centrifugal water chilling units. None of these panels are
now in production, this bulletin will provide general
information on these superseded panels to assist service personnel in understanding the operating sequence as well as providing control settings and
functions.
Each unit control oanel contained necessarv
operating
and
1.
Leaving Water Cycling Thermostat (CT or LRT)
2.
Guardistor Motor Protection
High Pressure Cutout (HP)
3.
4.
Low Pressure Cutout
5.
Oil Pressure Differential Switch (OD)
6.
High Oil Temperature Thermostat (OT or HOT)
7.
Vane Closed Switch (VD)
8.
Low Pressure Override Switch
9.
Oil Pump Time Delay Relay (OTD)
10.
Oil Pump Motor Capacitor
11.
Oil Pump Motor Contactor
Oil Pump Motor Overload Relays (OL)
12.
Electronic Control Module (Temperature and
13.
Current)
Generally, control item identifications and identifying
symbols on wiring diagrams were maintained the same
from panel to panel; however, there were cases where
a control with the same function did carry a different
symbol than had been used on similar panes of an
earlier design. The table of operating and safety controls starting on page 14 will identify controls and also
show where differences did exist.
Notes
1.
2.
3.
-
The information following is of a general nature
and applies to all control panels illustrated on
pages 4 through 6, except for the temperature/
motor load control modules. Details on the different control modules which were used are presented starting on page 7.
When functions covered by a specific control panel
differ from the write-up below, these differences
will be covered with the control panel details on
pages 4 through 6.
A control summary table is presented starting on
page 14, the summary contains the control identifications and other details of protection and operating controls used in the panels.
controls.
All panels basically included:
(GR)
(LP)
(LPO)
(1
M)
protective
OPERATING SEQUENCE
The following operating sequence generally applies to
control panels built through January 1, 1982. Informa-
/l/82
tion on panels utilized after 1
rent product manuals.
Assuming all interconnecting control and power wiring
connections to the panel are complete and the
off” switch is in the “on” position, the operating
controls will be allowed to call for unit operation.
is contained in cur-
“on-
NOTE
If power to the control panel is supplied
by a separate transformer, it should be
rated 2KVA with an inrush rating of
The disconnect switch in the power lines
supplying this transformer must be marked
to prevent the switch from being opened
and de-energizing the control circuit. Oil
heaters are required whenever the unit is
shut down. It is most important that power
is available to the heaters at all times the
unit is not operating.
An open section in the control circuit has been
provided for connection of chilled and condenser
water pump starter interlocks and flow switches.
The purpose of these interlocks is to prevent the
compressor from starting unless both chilled and
condenser water pumps are running and flow has been
established.
The cycling thermostat with its control bulb located in
the leaving chilled water line will, when cooling is required, close its contacts and energize the starting
sequence built into the control panel (assuming the
chilled water pump is running and flow has been established) closing of the cycling thermostat contacts will
first call for oil pump operation by energizing the pump
motor contactor and the oil cooler solenoid valve
through the clutch coil contacts on the oil time delay
relay (OTD).
Once the oil pump is running, two switches and a
timing relay must be satisfied before the compressor
will be allowed to start.
1.
The oil pressure differential switch will close when
the oil/suction pressure difference is 50 psig or
greater. If adequate oil pressure is not developed,
this switch will not close and the compressor will be
prevented from starting.
Before the compressor can start, the inlet guide
vanes must be closed. The vane closed position is
sensed by a pressure switch which is activated
when the unloader piston has moved the guide
vanes to the fully closed position
capacity). Until the vanes are in the minimum
load position, the compressor starting position in
the control circuit will not be energized.
The control circuit also incorporates a timing relay
(OPT) which will stop the oil pump if adequate oil
pressure is not developed or the compressor does
not start within 60 seconds from the closing of the
cycling thermostat.
Once adequate oil pressure has been developed and
the oil differential and vane closed switches have
closed, the condenser pump will be energized by the
condenser pump relay contacts (HWR). The condenser pump must cycle with the compressor. A
second set of condenser pump relay contacts com-
plete a circuit to the motor control relay(s) (MCR),
energizing it or them and as a result energizing the
compressor motor starter to bring the compressor on
line.
Once the compressor is running, the temperature
control module will direct the opening or closing of
the compressor suction inlet guide vanes as requirements for more or less cooling are relayed by the
sensor located in the leaving chilled water line.
12KVA.
(10
percent
2
In addition to temperature, the current section of the
control module is constantly monitoring the amount of
current being drawn by the compressor motor. The
current limit is manually set for the required current
limit level (percent of rated load amperes). Regardless
of demands for added cooling capacity, the current
sensing section of the module will not permit the
compressor vanes to open beyond the point where
added capacity will require a value of motor current
which would exceed the current limit setting.
When load conditions change and the need for less
cooling is relayed to the temperature control section
through the sensor in the leaving chilled water, compressor capacity will be reduced as the building
load drops. When the compressor has been unloaded
to 10 percent and the load continues to fall, leaving
chilled water temperature will also drop until the
setting of the cycling thermostat is reached
below design leaving water temperature), at this point
the contacts in the cycling thermostat will open and
the following sequence will take place:
1.
The condenser pump relay will be de-energized
and the condenser pump will stop.
The motor control relay will be de-energized,
2.
opening the compressor starter contacts and stopping the compressor.
The oil pump will continue to run for an additional
3.
30 seconds after the cycling thermostat contacts
open. Keeping the oil pump running after the compressor has stopped will accomplish the following:
a. Bearing lubrication is assured during the spin-
down period.
b. If the compressor cycled off before the vanes
were at minimum load position, the unloading
piston will be driven toward the minimum load
position. (The vanes must be at the minimum
load position before the compressor can start
on the next call for cooling.
4.
The compressor and oil sump heaters are energized
and stay on until the compressor starts again.
5.
A timing relay is incorporated into the control circuit to limit compressor starts to not more than one
every 40 minutes (timed from start). If the com-
pressor operating period prior to shutdown was
less than the time setting, it will be necessary for
the time remaining on the timer to elapse before
the compressor will be permitted to restart. If the
running time prior to shutdown was equal to or
greater than the time setting, the compressor will
be permitted to restart any time the cycling thermostat calls for cooling. A second type of relay was
used on later units where a 20 minute interval from
stop to start was utilized.
In
the event of a power failure during compressor
operation, the compressor bearings will be protected
by oil stored in the emergency cylinder. The spring
loaded piston in this cylinder will force oil into the
various lubrication passages and assure that all bear-
ings are lubricated during the
The exception to the above paragraph is the
through 135W units. These units utilized a solenoid
valve “SD” and condensing pressure to force oil
from the supply line,oil filter and oil cooler into
the compressor bearings.
GUARDISTOR
The compressor motor is protected by the Guardistor
MOTOR PROTECTION
)
spindown
period.
(3’F
PE095W
motor protection circuit. This circuit utilizes thermistors buried in the motor winding to sense temperature changes. At a preset temperature the resistance of the thermistor increases rapidly, this increase
in resistance and the resulting voltage drop causes the
guardistor relay to open and in turn to de-energize
relay
“Rl”
which opens the operating circuit and
energizes motor control relay (MCR).
The Guardistor circuit, once opened, requires manual
resetting before the compressor can be restarted. If
power to the control panel is interrupted for any
reason, the circuit will open and will have to be
manually reset once power is restored to the control
panel.
CAPACITY CONTROL MODULE
The capacity control module, regardless of the type
incorporated in the control panel, will perform the
functions described below. Where a given control
performs in a different manner, the differences will
be covered with details for that particular module
starting on page 7.
The control module is powered from a 5 volt supply
(through a current transformer and resistor located in
the compressor starter).
The control in response to signals relayed from a sen-
sor located in the leaving chilled water will regulate
compressor capacity by opening and/or closing two
solenoid valves “SA” (unload) and “SB” (load).
Opening and/or closing these valves permits oil pres-
sure to build up or drain from opposite ends of a
cylinder containing a floating piston. The compressor
suction inlet guide vanes are linked to the piston and
are positioned by moving it in one direction or the
other until the vane opening is adequate to satisfy
the load requirements.
The temperature control module on a call for increased
cooling capacity can continue to open the suction inlet
vanes until current drawn by the motor reaches the
setting of the current limit control. Once this current
value is reached, the current limit section of the control
will not permit additional loading of the compressor.
The current limit is adjustable from 40 to 100 percent
of rated load current.
The temperature controller can increase or decrease
compressor capacity through solenoid valves
and “SB”.
follows.
Loading
Unloading
Holding
Some older units included solenoid valve “SC”, this
valve was actuated by a low pressure switch and was
utilized to override the normal control and unload the
compressor on a sudden drop in suction pressure,
such as might be caused by a slow opening or sticking
expansion valve. On later units the “SC” valve was
eliminated and the low pressure override switch
actuated valve “SA” directly.
Most of the later panels included a service switch to
permit override of the capacity control and allow
manual control of compressor load level. This switch
has been included as a tool for the service mechanic
and should not be utilized for any other purpose.
3
The valve action to load or unload is as
-
SB energized, SA de-energized
-
SA energized, SB de-energized
-
SA and SB de-energized
de-
“SA”
Control Panels Used on Models
Through December
SOLID STATE
TEMPERATURE/CURRENT
LIMIT CONTROLLER
SEE PAGE 8
_,
PE063,079,100
31,1982
During the production life of this control
panel improvements were made. Among
these improvements were a number of
different temperature/current limit control
modules. The different modules used are
shown below with page references for
\
AND 126
ial
information.
TUBE TYPE
TEMPERATURE/
CURRENT LIMIT
CONTROLLER
SEE PAGE 7
NOTE
*%mii
I
SOLID STATE
TEMPERATURE/CURRENT
LIMIT CONTROLLER
SEE PAGE 11
1.
Panel power supply - l-60-1 15V
2. Disconnect switch in power supply to the control
panel must be on at all times. The oil heaters
receive power through this panel.
3. If panel power is supplied through a transformer,
it must have a minimum rating of 2 KVA with an
inrush of 12 KVA.
4. All panels incorporate a timer to limit starts to a
maximum of three (3) in a two hour period. (40
minutes between starts). Later panels 20 minutes
between stop and start.
5. Earlier versions of this panel included a high
discharge temperature cutout (“HDT”).
SOLID STATE
TEMPERATURE/CURRENT
LIMIT CONTROLLER
SEE PAGE 9
6. Later versions included a low oil temperature cutout
(“LOT”).
7. Later versions included a system monitor relay and
indicating light. The system monitor was utilized to
indicate a problem in the system external to the unit
control box. For example, the compressor starter
open because its overload relays have tripped.
8. Protection against damage caused by compressor
surging was added and a lockout relay and indicating light was incorporated on later versions of the
panel. This was labeled “Surg Gard”.
4
This Control Panel was used on all models PE075W through 135W units produced.
SOLID STATE
TEMPERATURE/
CURRENT LIMIT
CONTROLLER
SEE PAGE 11
THIS CONTROL
MODULE IS USED
AS A RETROFIT
DEVICE TO
REPLACE THE
ORIGINAL TUBE TYPE WHICH IS
NO LONGER AVAILABLE.
1. Panel power supply - 1-60-l
15V
2. The disconnect switch in the power supply to the
control panel must be on at all times. The oil
heaters receive power through this panel.
3. If panel power is supplied through a transformer,
it must have a minimum rating of 2 KVA with an
inrush of 12 KVA.
4. The control panel includes a time delay relay
limit compressor motor starts to a maximum of
three (3) in a two hour period. (40 minutes between
starts.
)
to
5. Panel includes a compressor start time delay relay
(CTD) which is set for 5 seconds. This permits oil
pressure to build up and bearings to be lubricated
prior to having the compressor start.
6. The compressor is protected during
spindown
after a power Failure by solenoid valve “SD”.
This is a normally open valve when its coil is
de-energized with this valve open condenser gas
pressure forces oil from the oil supply line and
compressor oil passages to assure bearing lubrication.
5
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