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Operation and Maintenance Manual OM 135
Group: Chiller
Part Number: 629956Y
Effective: November 1997
Supersedes: None
© 1997 McQuay International
PFS 155C through 315C
Operation and Maintenance Manual
50 and 60 Hertz
Refrigerant R-22 and Refrigerant R-410A
2 PFS 155C - 315C OM 135
Table of Contents
Unit Layout and Principles of Operation....................................................................3
Control Center....................................................................................................................................................3
Sequence of Operation......................................................................................................................................3
Start-up and Shutdown................................................................................................5
Pre Start-up.........................................................................................................................................................5
Start-up................................................................................................................................................................5
Temporary Shutdown........................................................................................................................................6
Start-up After Temporary Shutdown ..............................................................................................................6
Extended Shutdown...........................................................................................................................................6
Start-up After Extended Shutdown.................................................................................................................6
System Maintenance ..................................................................................................7
General.................................................................................................................................................................7
Lubrication System............................................................................................................................................7
Compressor Maintenance.................................................................................................................................7
Electrical Terminals ............................................................................................................................................8
Refrigerant Sightglass.......................................................................................................................................8
Lead-Lag..............................................................................................................................................................8
Crankcase Heaters .............................................................................................................................................9
Service.........................................................................................................................9
Compressor Solenoids......................................................................................................................................9
Filter-Dryers......................................................................................................................................................10
Pump-down.......................................................................................................................................................10
Liquid Injection Line Solenoid Valves ..........................................................................................................11
Electronic Expansion Valve.............................................................................................................................11
Electronic Expansion Valve Operation..........................................................................................................11
Evaporator.........................................................................................................................................................12
Condenser.........................................................................................................................................................12
Refrigerant Charging.......................................................................................................................................12
Liquid Presence Sensor...................................................................................................................................13
High Condenser Pressure Control.................................................................................................................13
Mechanical High Pressure Safety Control...................................................................................................13
Compressor Motor Protection.......................................................................................................................13
Phase/Voltage Monitor....................................................................................................................................14
Controls, Settings, and Functions.............................................................................15
200 Series MicroTech Control Panel.............................................................................................................15
Control Panel Layout.......................................................................................................................................16
Component Description..................................................................................................................................17
Keypad / Display Operation...........................................................................................................................22
Menu Structure ................................................................................................................................................26
MicroTech Menus.....................................................................................................27
Troubleshooting Chart ..............................................................................................43
Maintenance Schedules............................................................................................45
"McQuay" is a registered trademarks of McQuay International
1997 McQuay International
"Illustrations cover the general appearance of McQuay International products at the time of publication and we reserve the right to make changes in design and
construction at anytime without notice"
OM 135 PFS 155C - 315C 3
Unit Layout and Principles of Operation
Control Center
All electrical controls are enclosed in a control center with keylocked, hinged access doors. The
control center is composed of two separate compartments, MicroTech Controller and shelf-mounted
starter.
The MicroTech control panel contains a model 280 microprocessor based controller which provides all
monitoring and control functions required for the safe, efficient operation of the chiller. The operator
can monitor all operating conditions by using the panel’s built in 4-line by 40-character keypad /
display or by using an IBM compatible computer running McQuay Monitor software. In addition to
providing all normal operating controls, the MicroTech controller monitors all safety devices on the
unit and will take corrective action if the chiller is operating outside of it’s normal design conditions. If
a fault condition develops, the controller will shut the system down and activate an alarm output.
Important operating conditions at the time an alarm condition occurs are retained in the controller’s
memory to aid in troubleshooting and fault analysis.
The system is protected by a simple password scheme which only allows access by authorized
personnel. A valid password must be entered into the panel keypad by the operator before any
setpoints may be altered.
Sequence of Operation
The following sequence of operation is typical for McQuay models PFSXXXC screw water chillers.
The sequence may vary depending on the software revision or various options that may be installed
on the chiller.
Off conditions
With power supplied to the unit, 115 VAC power is applied through the circuit breaker (CB) to the
primary of the 24V control circuit transformer and Output Board Relays. The compressor heater (HTR)
is energized through the normally closed contacts on the starter. Note: Before start-up, the
compressor heater must be on for at least 12 hours to insure there is not any liquid refrigerant in the
compressors. The 115V / 24V transformer provides power to the MicroTech controller, two 24V center
tapped transformers and related components. With 24V power applied, the controller will check the
position of the front panel system switch. If the switch is in the “Stop” position the chiller will remain
off and the display will indicate the operating mode to be OFF: System Sw. (Be certain the individual
compressor switches inside the top right door are in the “on” position. These switches may be used
to lock out a specific compressor.) If the system switch is in the “Auto” position the controller will
then check the remote start/stop switch. If the remote start stop input is open, the chiller will be OFF:
RemoteSw. The chiller may also be commanded off via communications from a separate
communicating panel such as the Chiller System Controller Panel or an Open Protocol interface. The
display will show OFF: RemoteComm if this operating mode is in effect. If an alarm condition exists
which prevents normal operation, the chiller will be disabled and the display will indicate OFF: Alarm.
If the control mode on the keypad is set to “Manual Unit Off,” the chiller will be disabled and the unit
status will display OFF: Manual Mode. Assuming none of the above stop conditions are true, the
controller will examine the internal time schedule to determine whether the chiller should be permitted
to start. The operating mode will be OFF: TimeClock if the time schedule indicates time remaining in
an “off” time period.
Ice Mode Operation
For operations requiring ice mode feature, logic in MicroTech must be programmed to adjust the
operating parameters for the specific application . Refer to the control section of this manual for
additional information.
4 PFS 155C - 315C OM 135
Alarm
The alarm light on the MicroTech control panel will be illuminated when any alarm condition exists.
Unless the alarm condition affects both compressors, the remaining compressor will operate as
required. Refer to the control section of this manual for additional information.
Start-up
If none of the above “off” conditions are true, the MicroTech controller will initiate a start sequence
and energize the chilled water pump output relay. If flow is not proven within 15 seconds, the alarm
output will be turned on and the keypad display will be No Evap Flow. When evap flow is confirmed,
the controller will sample the chilled water temperature and compare it against the Leaving Chilled
Water Setpoint and the Start-up Delta Temperature, which have been programmed into the controller’s
memory. If the leaving chilled water temperature is above the Leaving Chilled Water Setpoint plus the
adjustable Start-up Delta Temperature (which is defined outside of the control band), the controller
will then start the condenser pump. The same time and alarm conditions exist for the condenser flow.
The compressor with the lowest number of starts will be the lead compressor. The controller will open
the electronic expansion valves to regulate the pressure difference between the evaporator and the
condenser by pulling the evaporator pressure low once the compressor starts. The controller will start
the lead compressor and energize the compressor suction injection and motor cooling solenoid valves.
Liquid injection is energized through the auxiliary starter contacts. The lead compressor will increase
capacity by staging up according to the chilled water leaving evap setpoint. The lead compressor will
stage to 100% capacity before starting the lag compressor. If additional cooling capacity is required,
the controller will energize the lag compressor and stage it up according to setpoint. The compressors
capacity control solenoids will automatically be controlled as required to meet the cooling needs of
the system.
The electronic expansion valves are operated by the MicroTech controller through adaptive control
strategies (use of different system temperatures and pressures) to maintain desired refrigerant control
to the evaporator at all conditions.
Condenser Control
The condenser pump will be started in conjunction with the above logic to provide condenser water
flow. The minimum entering condenser water temperature for full load air conditioning duty shall be
65°F with nominal cooling tower water flow of 3 GPM. When condenser water temperatures are lower
and or chiller load is less than 100%, the condenser water flow or entering condenser water
temperature must be controlled to maintain satisfactory operating refrigerant pressures. The
MicroTech controller can control condenser water entering temperature by a condenser water bypass
valve based upon entering condenser water temperature. It can also control condenser water flow by
a flow control valve based upon condenser pressure. When using a flow control valve, a minimum
water flow through the condenser must be maintained. This minimum water flow is based upon
system conditions and can vary with each installation.
Shutdown
As the system chilled water requirements lessen, the compressors will be unloaded. As the system
load continues to drop, the lag compressor (compressor with the most run hours) will be stopped. A
continuing load reduction will start the hot gas option or the chiller can shut down on the shut down
delta setpoint below the control band.
Hot gas control will allow the unit to maintain minimum operating parameters if proper condenser
control is available. This type of control is standard and selectable from the keypad. If hot gas
control is not selected, the unit will shut down on the shut down delta setpoint. This feature can be
used to minimize chiller run time under light load conditions.
The condenser water pump will be stopped upon chiller shutdown and the chilled water pump output
relay will remain energized until the time schedule’s “on” time expires, the remote stop switch is
opened, the system switch is moved to the stop position, or a separate communications panel such as
the Chiller System Controller or an Open Protocol interface disables the chiller.
OM 135 PFS 155C - 315C 5
Start-up and Shutdown
CAUTION
To ensure correct compressor rotation, field power supply leads must be properly phased
before start-up. A phase monitor protects the compressors after proper phasing has been
confirmed.
Pre Start-up
1. With all electric disconnects open, check all screw or lug type electrical connections to be sure
they are tight.
2. Check voltage of the unit power supply and verify voltage is within 10% of nameplate rating.
Voltage unbalance between phases must be within 3% of nameplate rating.
3. Make certain all auxiliary control equipment is operative and an adequate cooling load is available
for startup.
4. Check all compressor valve connections for tightness to avoid refrigerant loss at start-up. Open
the compressor suction and discharge shutoff valves. Open the liquid line shutoff valves until
backseated. Always replace valve seal caps.
5. Turn compressor circuit breakers to “off” position until ready to start unit. Place main power and
control disconnect switches in “on” position. This will energize compressor heaters. Wait at
least 12 hours before starting unit.
Note: Evaporator and condenser water should be chemically treated.
6. Vent air from the evaporator and condenser system piping. Open all water flow valves and start
chilled water and condenser water pumps. Check all piping for leaks. Flush the evaporator and
condenser water system piping to obtain clean, non-corrosive water in the chiller water circuits.
Start-up
1. Ensure compressor suction and discharge shutoff valves are fully open. Always replace valve
seal caps.
2. Ensure manual liquid line shutoff valves at the outlet of the condenser and liquid line dryer are
open.
3. Start the auxiliary equipment for the installation by turning on the time clock or remote on/off
switch or both.
4. Turn on both compressor switches. (Located under the top door.)
5. Under menu 7 of the keypad place the unit into the automatic mode. Place the front panel switch
into the auto position. Make the remote start / stop input.
6. Superheat is factory adjusted to maintain between 1° and 10°F (1° and 7°C).
6 PFS 155C - 315C OM 135
Temporary Shutdown
CAUTION
To prevent evaporator freeze-up, continue chilled water flow to the unit for 5 minutes after the
compressors have stopped.
If all power is turned off to the unit the compressor heaters will become inoperable. Once power is
resumed to the unit it is important that the compressor heaters are energized a minimum of 12 hours.
Failure to do so could damage the compressors due to excessive accumulation of liquid in the
compressor.
CAUTION
The unit must not be cycled off by using the evaporator pump or the disconnect switch. A
start / stop input is required.
Start-up After Temporary Shutdown
1. Ensure compressor heaters have been energized for at least 12 hours
2. Start the chilled water pump.
3. Place unit control switch in “auto” position.
4. Observe unit operation until the system has stabilized.
5. Record unit operating conditions.
Extended Shutdown
1. Place control panel switches in "stop" position.
2. After compressors have shut down and electronic expansion valves have closed, turn off chilled
water pump.
3. Turn off all power to the unit and to the chilled water and condenser water pumps.
4. Tag all opened disconnect switches to warn against accidental startup before completing
compressor checks.
5. If the unit is shut down during winter and glycol is not used in the system, drain all water from
unit evaporator, condenser and all water piping . Do not leave the vessels or piping open to the
atmosphere over the shutdown period.
Start-up After Extended Shutdown
1. Inspect all equipment to ensure a satisfactory operating condition.
2. Clean cooling tower. Remove all debris that has collected near the tower.
3. Place compressor suction and discharge valves in the fully open position. Always replace valve
seal caps.
4. Open manual liquid line shutoff valves.
5. Make certain that circuit breakers are in the "off" position.
6. Make certain control panel rocker switches are in "stop" position.
7. Place main power and control circuit disconnects in ”on” position.
8. Allow the crankcase heaters to operate for a least 12 hours.
OM 135 PFS 155C - 315C 7
9. Start chilled water and condenser water pumps and vent air from the water piping as well as the
evaporator and condenser water sides. Start the auxiliary equipment for the installation by
making the remote start / stop input.
10. Check resets of all safety controls.
11. Place unit circuit breakers in “on" position.
12. Place control panel switch in "auto" position.
13. After running the unit for a short time, verify there is no flashing in the refrigerant sightglass.
System Maintenance
General
Check the liquid line sightglasses and take condensing and suction pressure readings. Using the
MicroTech keypad, ensure the unit has normal superheat and subcooling readings.
The refrigerant temperatures and pressures (Menu 5 on MicroTech) allows the operator to determine if
the chiller is performing properly. Record these values in a chiller log daily. The values will change as
the load, condenser temperature and evaporator temperature vary. The operator should be able to
correlate displayed information to varying load conditions.
Lubrication System
Compressor Maintenance
The semi-hermetic compressor does not require an oil separator, oil heaters or pumps, so yearly
maintenance is not normally required. However, vibration is an excellent check for proper mechanical
operation. Excessive compressor vibration indicates maintenance may be required and contributes to
a decrease in unit performance and efficiency. Using a vibration analyzer, check compressor at or
shortly after start-up and again on an annual basis. When performing the test the maintain the load as
closely as possible to the load of the original test.
The compressor is checked at the factory for minimum vibration of 0.14”/second (3.56mm/
second) at 3500 rpm (2917 rpm).
The compressor is supplied with a lifetime oil filter. If a visual inspection shows possible
restriction, then replace filter.
8 PFS 155C - 315C OM 135
Electrical Terminals
WARNING
Electric shock hazard. Turn off all power before continuing with following service.
Re-tightened all electrical power terminals for compressors every six months (normal heating and
cooling of the wire may loosen connection).
Refrigerant Sightglass
Observe the refrigerant sightglasses weekly. A clear glass of liquid indicates that there is adequate
refrigerant charge in the system. Bubbling refrigerant in the sightglass, during stable run conditions,
indicates the system may be short of refrigerant charge. Refrigerant gas flashing in the sightglass
indicates an excessive pressure drop in the liquid line, possibly due to a clogged filter-dryer or a
restriction in the liquid line. If subcooling is low add charge to clear the sightglass. If subcooling is
normal 10° to 15°F (6° to 13°C), at full load, and flashing is visible in the sightglass check pressure
drop across the filter dryer.
An element inside the sightglass indicates the moisture condition corresponding to a given element
color. If the sightglass does not indicate a dry condition after about 12 hours of operation, pump
down the unit and change filter-dryers.
Lead-Lag
McQuay PFS water cooled chillers alternate the sequence in which the compressors start to balance
the number of starts and run hours. Lead-lag of the compressors is accomplished automatically by the
MicroTech controller.
When in the auto mode the compressor with the fewest number of starts will be started first. If
both compressors are operating and a stage down to one compressor is required, the compressor with
the most operating hours will cycle off first. The operator may override the MicroTech controller, and
manually select the lead compressor as #1 or #2.
OM 135 PFS 155C - 315C 9
Crankcase Heaters
The compressors are equipped with crankcase heaters. Crankcase heaters keep the temperature in the
crankcase high enough to prevent refrigerant from migrating to the crankcase and condensing in the
oil during the off-cycle.
Turn on power to the heaters for at least 12 hours before the compressors are started. The
crankcase temperature should be at least 80°F (26.7°C) before the system is started minimizing
lubrication problems of liquid slugging .
Service
Disconnect all power before doing any service inside the unit.
CAUTION
Service on this equipment is to be performed by qualified refrigeration personnel familiar with
equipment operation, maintenance, correct servicing procedures, and the safety hazard
inherent to this work. Causes for repeated tripping of safety controls must be investigated and
corrected.
Compressor Solenoids
The PFS unit screw compressors are equipped with three solenoids to control compressor capacity.
The solenoids are controlled by MicroTech outputs (see unit wiring diagrams). The solenoids are
energized at various compressor load conditions as indicated in Table 1.
Table 1, Solenoid status
Compressor Unloading Solenoid Staus
Percent Compressor Top Bottom Front Bottom Rear
Loading Solenoid Solenoid Solenoid
100 Energized Off Energized
75 Energized Energized Off
50 Off Off Energized
25 Off Energized Off
Location of the solenoids is as follows:
• The top solenoid is on top of the compressor near the discharge end.
• The bottom solenoids are on the lower side of the compressor on the opposite end from the
terminal box. The bottom front solenoid is the one closest to the discharge end of the
compressor. The bottom rear solenoid is the one closest to the motor end of the compressor.
If the compressor is not loading properly check the solenoids to see if they are energized. A complete
check will include a check of the MicroTech output, the wiring to the solenoid and the solenoid coil
itself.
10 PFS 155C - 315C OM 135
Filter-Dryers
Change the filter-dryer every scheduled service maintenance of the unit, or when any one of the
following conditions occur:
• Excessive pressure drop is read across the filter-dryer (The maximum recommended pressure drop
across the filter-dryer is shown in Table 2.
Table 2, Filter-dryer pressure drop
Maximum recommended pressure
drop
Percent Circuit Loading PSIG (kPa)
100 10 (69)
75 8 (55.2)
50 5 (34.5)
25 4 (27.6)
• When bubbles occur in the sightglass with normal subcooling
• A partially clogged filter causes a trip on the no liquid run sensor.
• Moisture indicating liquid line sightglass indicates excess moisture.
Pump-down
Note: Pump-down the unit before changing filter-dryer cores, replacing solenoid valves (except
solenoid valve coils), or to change expansion valve.
Unit condensers are sized to hold the entire refrigerant charge. Use method (A) or (B) below to pump-
down the unit.
A. Unit pump-down using the compressor.
1. Go to MicroTech menu number 16.
2. Select “Manual Pump-down”
3. Choose “YES”.
B. Unit Pump-down using a refrigerant transfer pump.
1. Stop the unit by opening the remote start / stop input.
CAUTION
Do not close any liquid line shutoff valves while unit is in operation. Liquid injection and
suction injection must be available at all times.
2. Close all liquid line shutoff valves at the condenser liquid line outlets.
3. When the compressor shuts off, close the discharge line ball valve in each compressor
circuit.
4. Connect a refrigerant transfer pump between the service valve on the evaporator and the
service valve on the top of condenser. Pump all remaining refrigerant out of evaporator,
compressors, and liquid line.
5. Complete pump-down according to EPA refrigerant guidelines before opening the circuit.
6. Servicing of the components may now continue.
OM 135 PFS 155C - 315C 11
WARNING
The discharge housing of the component contains internal discharge side check
valves. If these valves are tight seating, then this housing will contain high pressure
refrigerant captured between these check valves and the discharge line shutoff valve.
The MicroTech high pressure transducer should reflect this pressure. Be careful when
servicing the discharge housing.
Liquid Injection Line Solenoid Valves
The solenoid valves that shut off refrigerant flow during a power failure, do not normally require any
maintenance.
The solenoid coil can be checked to see that the stem is magnetized when energized by touching a
screwdriver to the top of the stem. If there is no magnetization either the coil is bad or there is no
power to the coil. The solenoid coil may be removed from the valve body without opening the
refrigerant piping. For personal safety shutoff and lockout the unit power.
The coil can then be removed from the valve body by simply removing a nut or snap-ring located at
the top of the coil. The coil can then be slipped off its mounting stud for replacement. Be sure to
replace the coil on its mounting stud before re-applying power.
Liquid injection is required during compressor operation to seal and cool the screw. A liquid injection
sensor is installed on the compressor to assure that liquid injection occurs whenever the compressor
is running. A failure of the liquid injection solenoid valve to open will cause the compressor to shut
down due to lack of liquid injection. The liquid injection solenoid valve only closes when the
compressor stops.
Electronic Expansion Valve
The expansion valve is responsible for allowing the proper amount of refrigerant to enter the
evaporator to match the cooling load. It does this by maintaining a constant superheat. (Superheat is
the difference between refrigerant temperature of the vapor as it leaves the evaporator and the
saturation temperature corresponding to the evaporator pressure).
All PFS chillers are factory set for the proper superheat. The superheat is controlled through adaptive
control strategies by the MicroTech controller and is not adjustable.
The expansion valve does not normally require maintenance, but if it requires replacement, follow the
same steps used to change a filter-dryer.
If the problem can be traced to the electric motor only, it can be unscrewed from the valve body
without removing the valve but only after pumping the unit down.
Electronic Expansion Valve Operation
There are three colored indicator LEDs (green, red, yellow) located in the control panel on the
electronic expansion valve (EXV) board. When the control panel is first powered the microprocessor
will automatically step the valve to the fully closed (shut) position and the indicator lights on the EXV
will blink in sequence. The valve can also be heard closing as it goes through the steps. The valve
will take approximately 14 seconds to go from a full open position to a full closed position.
The position of the valve can be viewed at any time by is using the MicroTech keypad through menu
3 (circuit pressures). There are a total of 760 steps between closed and full open.
12 PFS 155C - 315C OM 135
A feature of the electronic expansion valve is a maximum operating pressure setting (MOP). This
setting limits the load on the compressor during start-up periods where high return evaporator water
temperatures may be present. The valve will limit the maximum suction pressure at start-up to
approximately 85 psig (586 kPa). The valve will close to a point necessary to maintain the 85 psig (586
kPa). During this time the superheat will rise above 12°F (6.7°C) and not drop below 12°F (6.7°C) until
the suction pressure drops below 85 psig (586 kPa). The valve will maintain evaporator pressure close
to 85 psig (586 kPa) until the evaporator water temperature decreases to approximately 55°-60°F (12.8°-
15.6°C).
The valve remains closed at start and opens as the pressure between the condenser and evaporator
rises to control at a pressure ratio that assures good liquid feed to the compressors. At the end of the
cooling cycle the valve closes, partially pumping down the evporator. The valve closes at the rate of
approximately 55 steps per second, or from full open to full closed in approximately 14 seconds.
Evaporator
The evaporator is a flooded, shell-and-tube type with water flowing through the tubes and refrigerant
flowing through the shell over the tubes. Normally no service work is required on the evaporator.
When a tube must be replaced, the old tube can be removed and replaced. Follow the requirements
set forth by the EPA for the pumpdown and recovery of refrigerant.
Condenser
The condenser is a shell-and-tube type with water flowing through the tubes and refrigerant in the
shell. External finned condenser tubes are rolled into steel tube sheets. Integral subcoolers are
incorporated on all units. All condensers are equipped with two relief valves and a shutoff valve.
Either end on the condenser can be easily removed in the field.
Refrigerant Charging
PFS water-cooled screw chillers are shipped with a full operating charge of refrigerant. If a unit must
be field charged, follow these recommendations.
PFS water-cooled screw chillers are more sensitive to undercharging than to overcharging.
Therefore, it is preferable to be slightly overcharged rather than undercharged on a circuit. The
optimum charge is the charge that allows the unit to run with a solid stream of liquid in the liquid line
at all operating conditions. When the liquid line temperature does not drop with the addition of 5-10
lb. (2.3-4.5 kg) of charge then the subcooler is nearly full and proper charge has been reached. If the
liquid line temperature does not drop and the discharge pressure goes up 3-5 psig (21-35 kPa) as 5-10
lb. (2.3-4.5 kg) of refrigerant is added the correct maximum charge has been reached.
Unit charging can be done at any steady load condition. Unit must be allowed to run 5 minutes or
longer.
Note: As the unit changes load the subcooling will vary but should recover within several
minutes and should never show below 6°F (3.4°C) subcooling at any steady state run
condition. Subcooling will vary somewhat with evaporator leaving water temperature and
suction superheat. As the evaporator superheat goes lower the subcooling will drop slightly.
Excessive refrigerant losses can also leak oil from the system. When adding charge, add four
percent oil by weight. Use PLANETELF ACD 68AW oil.
A refrigerant leak in the unit could be very small and have little effect on system operation or
could be severe enough to cause the unit to shut down on a safety trip.
1. If the unit is slightly undercharged the unit will show bubbles in the sightglass. Recharge the
unit as described in the following charging procedure.
OM 135 PFS 155C - 315C 13
2. If the unit is moderately undercharged the unit will most likely trip on freeze protection. Recharge
the unit as described in the following charging procedure.
3. If the unit is severely undercharged the unit will trip off due to lack of liquid injection. In this case
either remove the remaining charge by means of a proper reclamation system and recharge the
unit with the proper amount of refrigerant as is stamped on the unit nameplate, or add refrigerant
through the suction valve back seat port on the compressor. Feed liquid into the suction valve
when the compressor is running. If the unit is severely undercharged the unit may nuisance trip
during this charging procedure. If this happens close off the refrigerant from the tank and restart
the unit. Once the unit has enough charge so that it does not trip out continue with the charging
procedure below.
Procedure to charge a moderately undercharged PFS unit:
Note: Refrigerant can be satisfactorily added at less than full load conditions (preferably above
50% unit load and steady state). Condensing temperature should be reasonably high and
characteristic of normal cooling tower type operation. Saturated suction temperatures should
also be at a value not higher than the design leaving chilled water temperature.
1. Connect a refrigerant drum to the service valve on evaporator -- OR -- to the backseat port on the
suction service valve on compressor.
2. Open refrigerant drum adding a "weighed-in" amount -- OR -- charge refrigerant during operation
of the compressor(s) until liquid line and liquid injection line sightglasses are clear.
Liquid Presence Sensor
Each compressor is equipped with a liquid sensor to assure that liquid flows to the compressor for
cooling and sealing during operation. The sensor will shutdown the compressor if liquid is not
sensed and discharge superheat increases over 5°F. At start-up the liquid sensor checks for excessive
liquid in the compressor and will delay (adjustable delay time of five minutes) start until the
compressor heater transfers the liquid out of the compressor and into the condenser. A liquid trip by
the sensor will produce an alarm message on the MicroTech display.
High Condenser Pressure Control
MicroTech is also supplied with high pressure transducers on each compressor. Although the main
purpose of the high pressure transducer is to maintain proper head pressure control, another purpose
is to convey a signal to the MicroTech control to stop the compressor in the event of an excessive rise
in discharge pressure. If the high condenser pressure control trips, the MicroTech must be manually
reset.
Mechanical High Pressure Safety Control
The high pressure safety control is a single pole pressure activated switch that opens on a pressure
rise. When the switch opens, the control relay circuit is de-energized stopping the compressors.
The control is mounted on the compressor ahead of the discharge shut off valve.
Compressor Motor Protection
The compressors are supplied with two types of motor protection.
Repeat overload trips under normal operation may indicate wiring or compressor motor problems. The
overloads are manual reset and must be reset at the overload as well as through MicroTech.
Also, the compressors have a solid-state Guardistor™ circuit which provides motor over temperature
protection. The Guardistor™ circuit has automatic reset but must also be reset through MicroTech.
14 PFS 155C - 315C OM 135
Phase/Voltage Monitor
The phase/voltage monitor provides protection against three-phase electrical motor loss due to power
failure conditions, phase loss, and phase reversal. Whenever any of these conditions occur, a contact
opens which de-energizes the starter.
CAUTION
Incorrect phase rotation will damage the compressor.
When proper power is restored, contacts close and MicroTech enables compressors for operation.
When three-phase power has been applied, the output relay should close and the “run light” should
come on. If the output relay does not close, perform the following tests.
1. Check the voltages between L1 - L2, L1 - L3 and L2 - L3. These voltages should be approximately
equal and within +6% of the rated three-phase line-to-line voltage.
2. If these voltages are extremely low or widely unbalanced check the power system to determine the
cause of the problem.
3. If the voltages are good, using a phase tester, verify that phases are in A, B and C sequence for
L1, L2 and L3. Correct rotation is required for compressor operation. If required to do so by
phase sequence, turn off the power and interchange any two of the supply power leads at the
disconnect.
4. Turn on the power. The output relay should now close after the appropriate delay.
OM 135 PFS 155C - 315C 15
Controls, Settings, and Functions
200 Series MicroTech Control Panel
General Description
The MicroTech control panel contains a model 280 microprocessor based controller which provides all
monitoring and control functions required for the safe, efficient operation of the chiller. The operator
can monitor all operating conditions by using the panel’s built
in 4-line by 40-character keypad / display or by using an IBM
compatible computer running McQuay Monitor software.
In addition to providing all normal operating controls, the
MicroTech controller monitors all safety devices on the
unit and will take corrective action if the chiller is
operating outside of it’s normal design conditions. If a fault
condition develops, the controller will shut the system down
and activate an alarm output. Important operating
conditions at the time an alarm condition occurs are retained
in the controller’s memory to aid in troubleshooting and fault
analysis.
The system is protected by a password scheme which only allows access by authorized personnel. A
password must be entered into the panel keypad by the operator before any setpoints may be altered.
Features of the Control Panel
• Control of leaving chilled water within an
adjustable control band.
• Readout of all temperature and pressure
readings.
• Automatic control of evaporator and condenser
pumps.
• Control of up to 2 stages of cooling tower fans
• Control of modulating cooling tower bypass valve.
• Control of modulating condenser water flow
valve.
• Panel mounted 12 key keypad plus 6 Quick
Access function keys. Operator can log chiller
operating conditions from a single keypad/display
instead of reading gauges, thermometers, pots,
etc. The display is a backlit, 4 line by 40
character LCD type for easy viewing in all lighting
conditions.
• Two levels of security protection against
unauthorized changing of setpoints and other
control parameters.
• Complete fault diagnostics to inform operators of
fault conditions in plain language. All faults are
time and date stamped so there is no guessing of
when the fault condition occurred. In addition, the
operating conditions that existed just before
shutdown can be recalled to aid in isolating the
cause of the problem.
• Five previous faults are available from the
display.
• Soft Loading feature reduces electrical
• Adjustable load pull-down rate reduces
undershoot during loop pulldown.
• Easy integration into building automation systems
via separate 4-20mAdc signals for chilled water
reset and demand limiting.
• Internal time-clock for on/off scheduling. The time
clock accommodates a 7 day schedule plus
holiday, 1 start and stop per day, and 14 holidays
with programmable duration.
• Communications capabilities for remote
monitoring, changing of setpoints, trend logging,
remote reset, alarm and event detection, via IBM-
PC running McQuay MicroTech
tm
software.
• Manual control mode allows the service
technician to command the unit to different
operating states. Useful for system checkout.
• Building Automation System communication
capability via McQuay’s Open Protocol strategy to
over 10 major BAS manufacturers.
• Service Test mode for troubleshooting controller
hardware.
• Keypad programmable alarm contacts for
normally open or normally closed.
• Pressure transducers for direct reading of
system pressures.
• Pre-emptive control of low evaporator pressure
conditions to take corrective action before a fault
trip.
• Pre-emptive control of high discharge
temperature.
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consumption and peak demand charges during
loop pulldown.
• Hot gas low load control
Control Panel Layout
Figure 1, Major Component Locations
Terminal
Block
Low Voltage Wireway
Signal
Converter
Signal
Converter
Guardister
Board
Guardister
Board
Low Voltage Wireway
Transformer T3
Transformer T4
AOX
Board
EXV
ModemLow Voltage Wireway
High
Press.
Relay
High
Press.
Relay
MCB 280
Output
Board
ADI
Board
Low Voltage Wireway
High Voltage Wireway
Terminal Block
Transformer
Circuit Breaker
OM 135 PFS 155C - 315C 17
Component Description
Microprocessor Control Board (MCB1)
The Model 280 Microprocessor Control Board contains the electronic hardware and software required
to monitor and control the unit. It receives input from the
ADI Board and sends commands to the Output Board to
maintain the unit's optimum operating mode for the current
conditions. Status lights are mounted on the control board
to indicate the operating condition of the microprocessor.
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Status LED’s
There are three status LED’s located on the model 280 controller which will indicate the
microprocessor’s operating condition. When power is first applied to the control panel, the red reset
LED will illuminate for approximately 3 seconds. During this time,
the microprocessor is checking the control software and
performing internal hardware tests. When these tests are
complete the reset LED will turn off and the green running LED
will illuminate indicating the controller’s circuitry and software are
operating correctly. The amber output 0 active LED is associated
with the external alarm output. This LED may or may not be
illuminated at this time based on the setpoints under menu 23.
If the reset LED stays on or the running LED fails to illuminate, disconnect the controller power
by opening circuit breaker CB-1 and re-check the field wiring. Observe the controller’s LED’s while re-
connecting power by closing CB-1. If the green running LED still does not turn on, a hardware failure
exists or the control software is corrupted. Downloading new control software or replacing the 280
controller should correct the problem.
With the controller powered up and the green running LED illuminated, the backlit panel on the
display module will be illuminated and the unit status menu will be visible. If the display text looks
faded or appears as “blocks” the contrast control needs to be adjusted. Watch the display and
adjusting the contrast control with a small flat-blade screwdriver until the best setting is determined.
Figure 2, Contrast adjustment
KDI BOARD
(back side)
Power
Wiring
Ribbon
Cable
Contrast
Adjustment
The MicroTech controller contains factory installed default setpoints which will be appropriate for
most common installations. Step through all of the unit’s setpoints by using the keypad / display and
adjust them as required to meet the specific job requirements. Any faults appearing on the display
should be cleared at this time by pressing the clear key.
green
red
amber
RUNNING
RESET
ACTIVE
CPU
STATUS
OUTPUT 0
OM 135 PFS 155C - 315C 19
Digital Output Board
The Output Board contains up to 24 solid state relays which are used to control the compressor,
cooling tower fans, solenoid valves and alarm annunciation. It receives control signals from the
Microprocessor Control Board through a 50 conductor ribbon cable.
Figure 3, Digital output board
Analog / Digital Input Board (ADI)
The ADI Board provides low voltage power for the temperature and pressure sensors. It also
provides optical isolation between the Microprocessor Control Board and all 24V switch inputs.
LED's are furnished on the board to give a visual indication of the status of all digital inputs. All
analog and digital signals from sensors, transducers and switches are received by the ADI Board and
then sent to the Microprocessor Control Board for interpretation.
Figure 4, ADI board
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Analog Output Board (AOX)
The AOX board converts control instructions from the Microprocessor Control Board’s expansion
bus into an analog control signal suitable for driving a cooling tower bypass valve. Each AOX board
is factory set via jumper to provide an output signal range of 0 - 10 VDC. An additional output on the
AOX board provides an analog signal that is proportional to compressor motor current.
Figure 5, AOX board
Signal Converter Board
The AC current signal generated by the starter is converted by the signal converter board into a 0-5
VDC signal that is directly proportional to the chiller amp draw. The amp draw signal is sent to the
ADI board for conditioning and then to the M280 controller.
Figure 6, Signal converter board
TB1 TB2
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