McQuay SEH 046 Installation Manual

INSTALLATION AND

MAINTENANCE DATA

WATER COOLED

CENTRIFUGAL CONDENSING

Models SEH

046,048,050,063,079,087

UNITS

& 100

Installation and maintenance are to be performed by qualified personnel who are familiar with local codes and regulations, and experienced with the type of equipment. are a potential injury hazard. Avoid contact with them.

CAUTION: Sharp edges and

coil

surfaces

GENERAL

The model SEH centrifugal condensing unit has been factory assembled, checked and shipped with holding charge of refrigerant.

The purchase price of this equipment includes checkout of the unit and initial startup by a McQuay service technician. An integral part of the startup procedure includes instruction of the responsible personnel in the operation and maintenance of this condensing unit.

It is most important that this equipment be properly operated and maintained if it is to perform the operating service it was designed and built to provide.

McQuay offers equipment maintenance and/or inspection programs that can be tailored to fit individual job requirements. Information on the various service programs is available through the McQuay Service Department or your local McQuay sales representative.

WARRANTY The McQuay model SEH condensing unit is covered by a standard published warranty which covers parts only. A complete published description of that warranty and its limitations is provided in a warranty certificate included with each unit.

First year warranty labor can be purchased separately. Check your local McQuay sales representative to establish what additional coverage (if any) was purchased for your unit.

INSTALLATION Information pertaining to the installation of model SEH condensing units is available in the installation bulletin A copy of this manual was included in the envelope shipped with the unit.

308.

UNIT NAMEPLATE Whenever requesting information or assistance on the model SEH condensing unit, the unit model number, shop order number and serial number should be copied from the unit

Figure 1. Figure

1 MODEL

STYLE SERIAL S.O. NO. SE1010

LBS. REFRIGERANT

I-

NOTE 1

model, style, serial, and shop order (SO.) numbers with your inquiry. NOTE 2

occurred; sample serial numbers follow:

Whenever inquiring about this unit please forward unit

On January 1, 1983, a change in serial number coding

l Through l After l/1183

SEH063JAUZlRKA2X

ISE1009GOl

5NA 1234500

FACTORY CHARGED

LEAK TEST PRESSURE

MOTOR COMPRESSOR CONTROLLER

AND OVERLOAD PROTECTION

SUPPLIED SEE SPEC PE-D4

111183 - LZ1320

5NA1234500

100 PSIG.

FIELD

is shown innameplate. A reproduction of this nameplate

UNIT MODEL DESIGNATION

COMPRESSOR

2 Compressor Size

3 Gear Ratio Code

4 Motor Electrical Power 5 Open-Drive Motor Description 6 Sound Control 7 Compressor Model Revision

-I-

SEH063KAR26RYYYBE26123B2RAAlO45OCCYA

01 02030405 0607060910

”

SEH WATER COOLED CENTRIFUGAL CONDENSING UNIT, HERMETIC

3 4 5

13 1415 16 1716 192021 222324

6 7

C22123CYY2RAYYYB1140OCCYYYYA

3738334041 4243 4445464746 495051 52 535455 56575659 6061 62 6364

MODEL CODING

EVAPORATOR

Evaporator Description

Tube Description

Head Description

Design Pressures 12 Leaving Water Temperature 13 Tube Sheet 14 Tube Cleaning System 15 Evaporator Model Revision

16 17 18 19

Head Material

9 10

252627 262930 313233 343536

CONDENSER

16 Condenser Description 17 Tube Description 18 Head Description 19 Design Pressures 20 Maximum Leaving Water Temp. 21 Tube Sheet 22 Tube Cleaning System 23 Condenser Model Revision

12 13 1415

Head Material

22 23

Page 4 I IM 309

OPERATING INFORMATION

OPERATOR’S REPONSIBILITY

Before operating the model SEH unit, become familiar with

the machine and accessory equipment.

If possible, arrange to attend a McQuay centrifugal

operator’s school.

After the unit has been checked out and approved for operation by a McQuay centrifugal service technician, work with him to learn how to prepare the system for start-

up. Start and stop the machine a number of times while observing the operation of the interlock function. The interlock circuit must be satisfied before the compressor will

run. After operating the unit, place it in the shutdown

mode.

Monitor operation and periodically inspect the equipment,

making routine adjustments where necessary.

Maintain a log of operating conditions on a daily basis. (Log sheets are available in pad form from McQuay.)

PRESTART SYSTEM CHECKLIST

NOTE: All of the following will have been checked out

by the McQuay startup technician during the initial

up procedure. Items preceded by an asterisk (*) should always be verified by the unit operator on a routine

basis during the operating season.

Unit:

*1.

All service valves in operating position.

*2.

Control circuit energized. Oil heaters have been operating for a minimum of 24

*3.

hours. Oil should be hot (approximately 130°F to

*4.

Oil charge visible in sightglass. (Mark level on sightglass while machine is shut down; check level weekly.)

Check control circuit. Verify that all safety switches in-

terrupt compressor starter holding coil.

Water flow through the condenser is correct. (This can be checked from condenser water pressure drop curves available from McQuay.) On any system, water flow can be reduced by a plugged strainer which can cause operating problems and nuisance tripouts. New systems are generally susceptible to blocked water strainers caused by foreign material washing out of the piping.

Electrical:

Wire size correct.

Phase sequence correct.

*3.

Voltage within plus or minus 10% of rated compressor

nameplate voltage.

*4.

Phase voltage unbalance 3% or less.

All wiring connections correct per unit wiring diagram.

All electrical connections tight and made with copper conductors and lugs.

All starter parts move freely and contacts meet evenly.

Motor overloads correct size. (Filled with dashpot oil,

sizes 079 and larger.) Do not attempt to field calibrate

adjustable overloads.

System:

‘1. Condenser pump rotating in right direction.

2. Condenser pump and motor lubricated.

start-

140°F).

*3.

All load equipment operative (main system fans, variable

volume boxes, etc.).

*4.

Tower fan(s) and controls operative.

*5. Tower water bleed and water treatment adequate.

STARTING When the 115 volt AC control power supply is applied to the control panel for the first time or after a power failure has occurred, the following will take place.

The oil sump heater(s) will be energized.

With “on-off” switch in either “on” or “off” position, its

indicating light will be out.

The external failure light will be lit. In addition, the exter-

nal alarm circuit will be de-energized indicating a unit

problem.

Push the reset button. The external failure light will go out and the external alarm circuit will be reset (de-energized). The pilot light in the “on-off” switch will now glow when the switch is pushed to “on.”

The unit safety circuits have now been reactivated and

5. the operating portion of the control circuit is ready to function.

A thermostat or other controller external to the unit panel

will, on a call for condensing unit operation, energize and close relay SR. (Relay SR is field supplied and is located external to the unit control panel.) Energizing this relay will close its contacts and:

Start the oil pump. When the oil pump develops oil pressure adequate to

close the oil differential pressure switch (50 psig above suction pressure), the switch will close.

A time delay relay PLT injects a 10 to 60 second time delay into the compressor starting control circuit and prevents this portion of the circuit from being energized while oil pressure is being developed. At the end of this delay, if the vane closed switch VC has closed, relay MCR (located in the unit starter) is energized as well as relay R3. The compressor starter will now close.

OPERATING

1. With the compressor running, capacity is controlled by positioning variable inlet vanes located in the suction gas inlet to the compressor. Opening the vanes allows the

compressor to pump more gas and, as a result, increases capacity. Closing the vanes-reduces gas flow and reduces capacity. The capacity control system is capable of

modulating the vane position to any capacity from 10%

to 100%.

The inlet vanes are controlled by means of four different devices. The capacity will be controlled by either temperature or pressure and the system design will determine whether “a” or always used on every unit.

a. A temperature sensor located in leaving airstream from

cooling coils or in leaving chilled water when a water chiller is used.

b. A suction pressure transducer, sensing system suction

pressure variations, translates changes in pressure into an electrical signal and through the control module loads or unloads the compressor (opens or closes the vanes).

“b”

below is used. Items “c” and

“d”

are

IM 309 I Page 5

c. The solid-state control module in conjunction with a cur-

rent transformer located in the compressor motor starter senses and will limit current drawn by the compressor motor, depending on the setting of the current limit control. This controller will override either control described in items “a” or motor current exceeds its setting, open or close the compressor vanes in response to changes in current. Whenever the motor current is less than the setting on the current limit controller, unit capacity control is returned to the temperature sensor or transducer. The current limit control can be set to limit current from 30% to 100% of nameplate full load current. The control is easily adjusted by a knob on the face of the control module.

d. The low pressure override switch LPO, built into the

unit control panel, senses suction pressure and is set to open at 2 to 5 psig above the low pressure safety switch. Whenever the setting is reached, the override switch opens and in turn opens control circuit of the temperature controller. This in turn energizes SA and de-energizes SB solenoids in the four-way valve. Full oil pressure is applied to the unloader piston driving the vanes closed. This action will in most cases catch a momentary “sudden” drop in suction pressure such as may be caused by a slow acting expansion valve, a drop that without this unloading feature would open the low pressure switch and stop the compressor. The LPO pressure switch is automatically reset; it will close when the pressure rises to a safe limit and return control of capacity to the temperature sensor or transducer.

3. During normal operation, the compressor will continue to operate and unload to a minimum of 10% until the cycl-

ing thermostat is satisfied. When this occurs, relay SR is de-energized. Opening relay SR will then cause the liquid line solenoid valve ahead of the expansion valves to close.

4. The unit control circuit incorporates a one-time arrangement. The compressor will continue to run after the system control thermostat is satisfied and has closed the liquid line solenoid valve. The compressor starter through the MCR relay is held in by a parallel circuit including a low pressure switch LPC and a set of normally open compressor motor starter auxiliary contacts (2Mb). As the compressor continues to run with the liquid line solenoid closed, the system suction pressure is reduced

“b”

above and will, whenever

ABl-#6.2

pumpdown

to the setting of cutout LPC, opening the switch and energizing relay MCR and stopping the compressor. The pressure switch LPC is automatically reset, but it cannot restart the compressor when its contacts reclose because the compressor starter auxiliary contacts 2Mb are now open. These contacts cannot reclose until the system sensor calls for cooling and energizes relay SR. Relay SR has a set of contacts in parallel with low pressure switch LPC and contacts 2Mb. These SR contacts when closed will permit the operating portion of the control circuit to call for the compressor to run.

5. The unit oil pump will continue to run for a minimum of one minute after the compressor starter has been energized. This will assure adequate lubrication for the compressor during the

In addition, on the next call for cooling, the compressor capacity control vanes must be in a closed position before the compressor is allowed to restart. Contacts VD (auxiliary contacts located in the compressor starter) signal the unload portion of the unit capacity control circuit and, if the vanes were not fully closed when the compressor was stopped, continues to energize solenoid SA and drive the vanes to the closed position while the pump is still running. This will then permit the compressor to start on the next call for cooling with a minimum delay. (The compressor will not start unless the vanes are in the closed position.)

6. Rapid cycling of centrifugal compressor motors is not desirable. A time delay through relay TDR is built into the unit control circuit to prevent rapid cycling. Relay TDR will prevent the compressor from restarting for a period of 20 minutes after the compressor is stopped unless the “automatic restarter after power failure with reduced timed off cycle” accessory option is used.

7. In the event of a power interruption during unit operation, the compressor is protected against damage by an emergency oil reservoir and spring load piston. During normal operation enough oil is stored in the emergency cylinder to lubricate the bearings during spindown. The oil is forced into the various passages by a spring loaded piston contained and compressed in the emergency oil cylinder. The spring is compressed by normal machine

oil pressure while the compressor is running and on a loss of power is available along with the piston to act as an emergency oil pumping device.

spindown

period.

de-

Page 6 I IM 309

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