McQuay PFS 155C, PFS 315C Maintenance Manual

Operation and Maintenance Manual OM 135

PFS 155C through 315C

Operation and Maintenance Manual 50 and 60 Hertz Refrigerant R-22 and Refrigerant R-410A

Group: Chiller Part Number: 629956Y Effective: November 1997

Supersedes: None

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

"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

2 PFS 155C - 315C OM 135



1997 McQuay International

construction at anytime without notice"

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.

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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.

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Start-up and Shutdown

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.

CAUTION

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).

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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.

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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.

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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.

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Service

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 .

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.

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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 pumpdown 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.

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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.

OM 135 PFS 155C - 315C 11

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.

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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.

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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.

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Controls, Settings, and Functions

200 Series MicroTech Control Panel

General Description

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 IBMPC running McQuay MicroTechtm 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.

OM 135 PFS 155C - 315C 15

+ 35 hidden pages

McQuay PFS 155C, PFS 315C Maintenance Manual

Specifications and Main Features

Frequently Asked Questions

User Manual