Trane CenTraVac Duplex CDHF Troubleshooting guide

CDHF-SVU01C-ENX39640670030
Operation
Maintenance
Duplex CDHF, CDHG
Water Cooled CenTraVac™
With CH530

© 2005 American Standard All rights reserved CDHF-SVU01C-EN
Warnings and
Cautions
Warnings and Cautions
Notice that warnings and cautions
appear at appropriate intervals
throughout this manual. Warnings
are provided to alert installing
contractors to potential hazards that
could result in personal injury or
death, while cautions are designed to
alert personnel to conditions that
could result in equipment damage.
Your personal safety and the proper
operation of this machine depend
upon the strict observance of these
precautions.
NOTICE:
Warnings and Cautions appear at appropriate sections throughout this manual.
Read these carefully.


WARNING – Indicates a potentially hazardous situation which, if not avoided, could result in
death or serious injury.


CAUTION – Indicates a potentially hazardous situation which, if not avoided, may result in
minor or moderate injury. It may also be used to alert against unsafe practices.
CAUTION – Indicates a situation that may result in equipment or property-damage-only accidents.

3
Contents
CDHF-SVU01C-EN
Warnings and Cautions
General Information
Unit Control Panel (UCP)
Operator Interface
Chilled Water Setpoint
Inter Processor Communication (IPC)
Control System Components
Controls Sequence of Operation
Machine Protection and Adaptive Control
Unit Startup
Unit Shutdown
Periodic Maintenance
Oil Maintenance
Maintenance
Forms
2
4
28
30
38
51
52
67
72
89
91
92
95
97
104

CDHF-SVU01C-EN
4
Typical Product Description Block
MODL CDHF DSEQ 2R NTON 2500 VOLT 575 REF 123
HRTZ 60 TYPE SNGL CPKW 142 CPIM 222 TEST AIR
EVTM IECU EVTH 28 EVSZ 032S EVBS 280
EVWC STD EVWP 2 EVWT NMAR EVPR 150
EVCO VICT EVWA LELE CDTM IECU CDTH 28
CDSZ 032S CDBS 250 CDWC STD CDWP 2
CDWT NMAR CDPR 150 CDCO VICT CDWA LELE
CDTY STD TSTY STD ECTY WEOR ORSZ 230
PURG PURE WCNM SNMP SPKG DOM OPTI CPDW
HHOP NO GENR NO GNSL NO SOPT SPSH
ACCY ISLS HGBP WO LUBE SNGL AGLT CUL
CNIF UCP SRTY USTR SRRL 207 PNCO TERM
General
Information
Unit Nameplate
The unit nameplate is located on the
left side of the unit control panel.
The following information is
provided on the unit nameplate.
1. Serial Number
The unit serial number provides the
specific chiller identity. Always
provide this serial number when
calling for service or during parts
identification..
2. Service Model Number
The service model represents the unit
as built for service purposes . It
identifies the selections of variable
unit features required when ordering
replacements parts or requesting
service.
Note: Unit-mounted starters are
identified by a separate number
found on the starter.
3. Product Coding Block
The CDHF and CDHG models are
defined and built using the product
definition and selection (PDS)
system. This system describes the
product offerings in terms of a
product coding block which is made
up of feature categories and feature
codes. An example of a typical
product code block is given on this
page. The coding block precisely
identifies all characteristics of a unit.
4. Identifies unit electrical
requirements
5. Correct operating charges and type
of refrigerant
6. Unit Test Pressures and Maximum
Operating Pressures
7. Identifies unit Installation and
Operation and Maintenance manuals
8. Drawing numbers for Unit Wiring
Diagrams
Literature change
Applicable to CDHF, CDHG
About this manual
Operation and maintenance
information for models CDHF, CDHG
are covered in this manual. This
includes both 50 and 60 Hz. CDHF
and CDHG centrifugal chillers
equipped with the Tracer CH530
Chiller Controller system. Please note
that information pertains to all three
chiller types unless differences exist
in which case the sections are
broken down by Chiller type as
applicable and discussed separately.
By carefully reviewing this
information and following the
instructions given, the owner or
operator can successfully operate
and maintain a CDHF, or CDHG unit.
If mechanical problems do occur,
however, contact a qualified service
organization to ensure proper
diagnosis and repair of the unit.

5
CDHF-SVU01C-EN
General
Information
Model Number - An example of a
typical duplex centrifugal chiller
model number is:
CDHF2100AA0BC2552613C0B203B0
B20KJAC1GW40C111340A010
Digit: Description
1st-2nd CD = CenTraVac®Duplex - 2
compressors
3rd H =Direct Drive
4th F = Development Sequence
(F - 2 Stage) (G - 3 Stage)
5th-8th 2100 = Nominal total
compressor tonnage
9th A = Unit Voltage
A = 380V-60Hz-3Ph
B = 440V-60Hz-3Ph
C = 460V-60Hz-3Ph
D = 480V-60Hz-3Ph
E = 575V-60Hz-3Ph
F = 600V-60Hz-3Ph
G = 2300V-60Hz-3Ph
H = 2400V-60Hz 3Ph
J = 3300V-60Hz-3Ph
K = 4160V-60Hz-3Ph
L = 6600V-60Hz-3Ph
M = 380V-50Hz-3Ph
N = 400V-50Hz-3Ph
P = 415V-50Hz-3Ph
R = 3300V-50Hz-3Ph
T = 6000V-50Hz-3Ph
U = 6600V-50Hz-3Ph
10th-11th A0 = Design Sequence
12th B = Compressor Motor
Power, LH Circuit
13th C = Compressor Motor
Power, RH Circuit.
Compressor Motor codes:
A = 588 KW
B = 653 KW
C = 745 KW
D = 856 KW
E = 957 KW
F = 1062 KW
G = 1228 KW
H = 433 KW
J = 489 KW
K = 548 KW
L = 621 KW
M = 716 KW
N = 799 KW
P = 892 KW
R = 403 KW
S = 453 KW
T = 512 KW
U = 301 KW
V = 337 KW
W = 379 KW
X = 1340 KW
14th-16th 255 = Compressor Impeller
Diameter LH Circuit
17th-19th 261 = Compressor Impeller
Diameter RH Circuit
20th 3 = Evaporator Tube Bundle
Size
1 = 2100 nominal ton
evaporator
2 = 2300 nominal ton
evaporator
3 = 2500 nominal ton
evaporator
4 = 1610 nominal ton
evaporator
5 = 1850 nominal ton
evaporator
21st C = Evaporator Tubes
A = I/E copper, 0.028” wall, 0.75” O.D.
B = I/E copper, 0.035” wall, 0.75” O.D.
C = S/B copper, 0.028” wall, 0.75”
O.D.
D = S/B copper, 0.035” wall, 0.75”
O.D.
E = I/E copper, 0.028” wall, 1.0” O.D.
F = I/E copper, 0.035” wall, 1.0” O.D.
22nd 0 = Not Assigned
23rd B - Evaporator Waterbox
A = 150 psig 1 pass marine
B = 300 psig 1 pass marine
C = 150 psig 1 pass non-marine
D = 300 psig 1 pass non-marine
24th 2 = Evaporator Waterbox
Connection;
1 = Victaulic
2 = Flanged
25th 0 = Not Assigned
26th 3 = Condenser Tube Bundle Size
1 = 2100 nominal ton condenser
2 = 2300 nominal ton condenser
3 = 2500 nominal ton condenser
4 = 1610 nominal ton condenser
5 = 1760 nominal ton condenser
6 = 1900 nominal ton condenser
27th B = Condenser Tubes
A = I/E copper, 0.028” wall, 0.75” O.D.
B = I/E copper, 0.035” wall, 0.75” O.D.
C = S/B copper, 0.028” wall, 0.75”
O.D.
D = S/B copper, 0.035” wall, 0.75”
O.D.
E = I/E copper, 0.028” wall, 1.0” O.D.
F = I/E copper, 0.035” wall, 1.0” O.D.
G = I/E 90/10 CU/NI, 0.035” wall,
0.75” O.D.
28th 0 = Not Assigned
29th B = Condenser Waterboxes
A = 150 psig 1 pass marine
B = 300 psig 1 pass marine
C = 150 psig 1 pass non-marine
D = 300 psig 1 pass non-marine
30th 2 = Condenser Waterbox
Connection;
1 = Victaulic
2 = Flanged
31st 0 = Not Assigned
32nd K = Orifice Size, LH Circuit,
33rd J = Orifice Size, RH Circuit,
Orifice Nominal Tons:
A = 710
B = 790
C = 880
D = 990
E = 1100
F = 1265
G = 1400
H = 1540
K = 1810
J = 1660
L = 1970
M = 2150
N = 1045
P = 1185
R = 1335
T = 1605
U = 1735

CDHF-SVU01C-EN
6
General
Information
V = 1890
W = 2060
X = 1475
Z = 560 - 3 stage 935 - 2 stage
Y = 500 - 3 stage 835 - 2 stage
1 = 630 - 3 stage 2245 - 2 stage
2 = 800 - 3 stage 2345 - 2 stage
3 = 900 - 3 stage 2450 - 2 stage
4 = 1000 - 3 stage 2560 - 2 stage
5 = 1120 - 3 stage 2675 - 2 stage
6 = 1250
7 = 1600
8 = 1800
9 = 750
34th A = Starter Type
A = Star-Delta Unit Mounted
C = Star Delta Remote Mounted
E = X-Line Full Volt Remote Mounted
F = Autotransformer Remote
Mounted
G = Primary Reactor Remote
Mounted
H = X-Line Full Volt Unit Mounted
J = Autotransformer Unit Mounted
K = Primary Reactor Unit Mounted
L = Solid State Unit Mounted
M = Solid State Floor Mounted
N = Solid State Wall Mounted
P = Adaptive Freq. Drive-Unit
Mounted
R = Customer Supplied
35th C = Control Enclosure;
C = Standard
S = Special
36th 1 = Control: Enhanced Protection;
0 = None
1 = Enhanced protection
37th G = Control: Generic BAS;
0 = None
G = Generic BAS
38th W = Water Flow Control;
0 = None
W = Water flow control
39th 4 = Tracer®Comm. Interface
0 = None, 4 = COMM 4,
5 = COMM 5, S = Special
40th C = Control: Condenser
Refrigerant Pressure;
0 = None, C = with
41st 1 = Control: Extended Operation;
0 = None
1 = Extended operation
42nd 1 = Chilled Water Reset -
Outdoor Air Temperature Sensor
0 = None,
1 = Chilled water reset – with outdoor
air temperature sensor,
S = Special
43rd 1 = Control: Operating Status,
0 = None,
1 = Operating Status
44th 1 = Gas Powered Chiller;
0 = No
1 = Yes
45th 3 = Compressor Motor Frame
Size LH Circuit
46th 4 = Compressor Motor Frame
Size RH Circuit
FRAME SIZE CODES: 3 = 440E, 4 =
5000, 5 = 5800, 6 = 5800L, S = Special
47th 0 = Unit Insulation;
0 = None
1 = Insulation package
48th A = Spring Isolators
0 = No
A = Yes
49th 0 = Not Assigned
0 = Not assigned
50th 1 = Evaporator & Condenser Size
1 = 210D - 2100,
2 = 250D – 2500,
3 = 250X - 2500 ,
4 = 250M - 2500
51st 0 = Special Options
0 = None
S = Special Option

7
CDHF-SVU01C-EN
General
Information
Commonly Used Acronyms
For convenience, a number of
acronyms are used throughout this
manual. These acronyms are listed
alphabetically below, along with the
“translation” of each:
AFD = Adaptive Frequency Drive
ASME = American Society of
Mechanical Engineers
ASHRAE = American Society of
Heating, Refrigerating and Air
Conditioning Engineers
BAS = Building Automation System
CABS = Auxiliary Condenser Tube-
Bundle S
CDBS = Condenser Bundle Size
CDSZ = Condenser Shell Size
CH530 = Tracer CH530 Controller
DV = DynaView™Clear Language
Display, also know as the Main
Processor (MP)
CWR = Chilled Water Reset
CWR’ = Chilled Water Reset Prime
DTFL = Design Delta-T at Full Load
(i.e., the difference between entering
and leaving chilled water
temperatures)
ELWT = Evaporator Leaving Water
Temperature
ENT = Entering Chilled Water
Temperature
GPM = Gallons-per-minute
HGBP = Hot Gas Bypass
HVAC = Heating, Ventilating, and Air
Conditioning
IE = Internally-Enhanced Tubes
IPC = Interprocessor Communication
LBU = La Crosse Business Unit
LCD = Liquid Crystal Display
LED = Light Emitting Diode
MAR = Machine Shutdown Auto
Restart (Non-Latching where chiller
will restart when condition corrects
itself.)
MMR = Machine Shutdown Manual
Restart (Latching where chiller must
be manually reset.)
MP = Main Processor
PFCC = Power Factor Correction
Capacitor
PSID = Pounds-per-Square-Inch
(differential pressure)
PSIG = Pounds-per-Square-Inch
(gauge pressure)
UCP = Unit Control Panel
LLID = Low Level Intelligent Device
(Sensor, Pressure Transducer, or
Input/output UCP module)
RLA = Rated Load Amps
RTD = Resistive Temperature Device
Tracer CH530 = Tracer CH530
controller
TOD = Temperature Outdoor
Control Optional Packages
OPST Operating Status Control
GBAS Generic Building Automation
Interface
EXOP Extended Operation
CDRP Condenser Pressure
Transducer
TRMM Tracer Communications
WPSR Water pressure sensing
EPRO Enhanced Protection
CWR Chiller Water reset outdoor

CDHF-SVU01C-EN
8
General
Information
Figure 1. General Duplex unit components - front view
Overview
CDHF - CDHG
See Figure 1 for General Unit
components. Each Chiller unit is
composed of the following
components as viewed when facing
the control panel front side:
• Common Evaporator and Common
Condenser
• Compressors and Motor 1 (Left
hand), and 2 (Right hand)
• Economizers 1(LH), and 2 (RH),
• Purge 1(LH), and 2 (RH),
• Oil Tank/ Refrig. Pump 1 (LH), and 2
(RH),
• Control Panel 1 (LH), and 2 (RH)
• And when specified Unit mounted
Starters 1 (LH) and 2 (RH) (not
shown).

9
CDHF-SVU01C-EN
General
Information
Figure 2. General Duplex unit components (2 stage compressor)

CDHF-SVU01C-EN
10
General
Information
Cooling Cycle
Duplex Chillers have two refrigerant
circuits that operate as their own
independent circuits. These circuits
are discussed as individual chiller
refrigeration units in the following
discussion. The sequence of
operation of the two refrigeration
circuits is discussed in a later
section.
When in the cooling mode, liquid
refrigerant is distributed along the
length of the evaporator and sprayed
through small holes in a distributor
(i.e., running the entire length of the
shell) to uniformly coat each
evaporator tube. Here, the liquid
refrigerant absorbs enough heat from
the system water circulating through
the evaporator tubes to vaporize.
The gaseous refrigerant is then
drawn through the eliminators
(which remove droplets of liquid
refrigerant from the gas) and first-
stage variable inlet guide vanes, and
into the first stage impeller.
Note: Inlet guide vanes are designed
to modulate the flow of gaseous
refrigerant to meet system capacity
requirements; they also prerotate the
gas, allowing it to enter the impeller
at an optimal angle that maximizes
efficiency at all load conditions.
Compressor 1 or 2 (3 Stage)
Compressed gas from the first-stage
impeller flows through the fixed,
second-stage inlet vanes and into the
second-stage impeller.
Here, the refrigerant gas is again
compressed, and then discharged
through the third-stage variable guide
vanes and into the third stage
impeller.
Once the gas is compressed a third
time, it is discharged into the
condenser. Baffles within the
condenser shell distribute the
compressed refrigerant gas evenly
across the condenser tube bundle.
Cooling tower water circulated
through the condenser tubes absorbs
heat from the refrigerant, causing it to
condense. The liquid refrigerant then
passes through orifice plate ‘‘A’’ and
into the economizer.
The economizer reduces the energy
requirements of the refrigerant cycle
by eliminating the need to pass all
gaseous refrigerant through three
stages of compression. See Figure 3.
Notice that some of the liquid
refrigerant flashes to a gas because
of the pressure drop created by the
orifice plates, thus further cooling the
liquid refrigerant. This flash gas is
then drawn directly from the first
(Chamber A) and second (Chamber
B) stages of the economizer into the
third-and second-stage impellers of
the compressor, respectively.
All remaining liquid refrigerant flows
through another orifice plate ‘‘C’’ to
the evaporator.
Compressor 1 or 2 (2 Stage)
Compressed gas from the first-stage
impeller is discharged through the
second-stage variable guide vanes
and into the second-stage impeller.
Here, the refrigerant gas is again
compressed, and then discharged
into the condenser.
Baffles within the condenser shell
distribute the compressed refrigerant
gas evenly across the condenser
tube bundle. Cooling tower water,
circulated through the condenser
tubes, absorbs heat from the
refrigerant, causing it to condense.
The liquid refrigerant then flows out
of the bottom of the condenser,
passing through an orifice plate and
into the economizer.
The economizer reduces the energy
requirements of the refrigerant cycle
by eliminating the need to pass all
gaseous refrigerant through both
stages of compression. See Figure 6.
Notice that some of the liquid
refrigerant flashes to a gas because
of the pressure drop created by the
orifice plate, thus further cooling the
liquid refrigerant. This flash gas is
then drawn directly from the
economizer into the second-stage
impellers of the compressor.
All remaining liquid refrigerant flows
out of the economizer, passes
through another orifice plate and into
the evaporator.

11
CDHF-SVU01C-EN
Figure 3. Pressure enthalpy curve (3 stage compressor)
Figure 4. 2-stage economizer (3 stage compressor)
General
Information

CDHF-SVU01C-EN
12
Figure 5. Pressure enthalpy curve (2 stage compressor)
Figure 6. Single stage economizer (2 stage compressor)
General
Information

13
CDHF-SVU01C-EN
Overview
Controls Operator Interface
Information is tailored to operators,
service technicians and owners.
When operating a chiller, there is
specific information you need on a
day-to-day basis — setpoints, limits,
diagnostic information, and reports.
When servicing a chiller, you need
different information and a lot more
of it — historic and active
diagnostics, configuration settings,
and customizable control algorithms,
as well as operation settings.
By providing two different tools –
one for daily operation and one for
periodic service — everyone has
easy access to pertinent and
appropriate information.
General
Information
DynaView™Human Interface
— For the operator
Day-to-day operational information is
presented at the panel. Up to seven
lines of data (English or SI units) are
simultaneously displayed on the ¼
VGA touch-sensitive screen.
Logically organized groups of
information — chiller modes of
operation, active diagnostics,
settings and reports put information
conveniently at your fingertips. See
Operator Interface Section for details.
TechView™Chiller Service Tool
— For the service technician or
advanced operator
All chiller status, machine
configuration settings, customizable
limits, and up to 60 active or historic
diagnostics are displayed through
the service tool interface. Without
changing any hardware, we give you
access to the latest and greatest
version of Tracer CH530! A new level
of serviceability using the innovative
TechView™chiller service tool. A
technician can interact with an
individual device or a group of
devices for advanced
troubleshooting. LED lights and their
respective TechView™indicators
visually confirm the viability of each
device. Any PC that meets the system
requirements may download the
service interface software and Tracer
CH530 updates. For more information
on TechView™visit your local Trane
Service company, or The Trane
Company’s website at
www.trane.com.

CDHF-SVU01C-EN
14
General
Information
CTV Duplex Sequence Of Operation
This section will provide basic
information on chiller operation for
common events. With
microelectronic controls, ladder
diagrams cannot show today’s
complex logic, as the control
functions are much more involved
than older pneumatic or solid state
controls. Adaptive control algorithms
can also complicate the exact
sequence of operation. This section
and its diagrams attempt to illustrate
common control sequences.
The Sequence of Events diagrams
use the following KEY:
Software States: (Figure 7)
There are five generic states that the
software can be in:
1. Power Up, Stopped, Starting,
Running, Stopping
Timeline Text: (Figures 8-11)
The large timeline cylinder indicates
the upper level operating mode, as it
would be viewed on DynaView. Text
in Parentheses indicates sub-mode
text as viewed on DynaView. Text
above the timeline cylinder is used to
illustrate inputs to the Main
Processor. This may include User
input to the DynaView Touch pad,
Control inputs from sensors, or
Control Inputs from a Generic BAS.
Boxes indicate Control actions such
as Turning on Relays, or moving the
Inlet Guide Vanes. Smaller cylinders
indicate diagnostic checks, Text
indicates time based functions, Solid
double arrows indicate fixed timers,
Dashed double arrows indicate
variable timers
Power Up Diagram:
The Power up chart shows the
respective DynaView screens during
a power up of the main processor.
This process takes from 30 to 50
seconds depending on the number
of installed Options. On all power
ups, the software model always will
transition through the ‘Stopped’
Software state independent of the last
mode. If the last mode before power
down was ‘Auto’, the transition from
‘Stopped’ to ‘Starting’ occurs, but it
is not apparent to the user.
Software Operation Overview
Diagram:
The Software Operation Overview is
a diagram of the five possible
software states. This diagram can be
thought of as a State Chart, with the
arrows, and arrow text, depicting the
transitions between states.
The text in the circles are the internal
software designations for each State.
The first line of text in the Circles are
the visible top level operating modes
that can be displayed on Dyna View.
The shading of each software state
circle corresponds to the shading on
the timelines that show the state that
the chiller is in.
Figure 7. Sequence of operation overview.

15
CDHF-SVU01C-EN
General
Information
Figure 8. CDHE/F/G sequence of operation: auto to running
This diagram shows the sequence of
operations for a start of the first
compressor on a duplex chiller. The
‘First’ compressor will be determined
by the type of duplex start selected.
Staging Second Compressor On:
This diagram shows the sequence of
operations where the ‘First’
compressor is all ready running, and
the ‘second’ compressor is staged
on. The ‘First’ and ‘Second’
compressor will be determined by
the type of duplex start selected
Figure 9. CDHE, CDHF, and CDHG sequence of operation: running

CDHF-SVU01C-EN
16
General
Information
Figure 11. CDHE, CDHF and CDHG sequence of operation: normal shutdown to stopped and run inhibit
Figure 10. CDHE/F/G sequence of operation: staging second compressor off
Staging Second Compressor Off:
This diagram shows the sequence of operations where there is no longer a need to run the ‘Second’ compressor, so it
is staged off. The ‘First’ and ‘Second’ compressor will be determined by the type of duplex start selected
Satisfied Setpoint:
This diagram shows the sequence of operations where the setpoint has been satisfied, and the last compressor is
staged off.

17
CDHF-SVU01C-EN
General
Information
Duplex Compressor Sequencing
Four methods (Two fixed sequence
methods, a balanced start and hour’s
method, and a no staging method)
are provided for order of a
compressor sequencing on CTV
Duplex chillers. The desired method
is selectable at startup via the service
tool. The application can decide to
either balance the wear burden
among the unit’s compressors, to
start the most efficient compressor,
or to simultaneously start and stop
both compressors to minimize
startup pull down time. Each method
has specific applications were it can
be used advantageously.
If one compressor is locked out, in
restart inhibit, or generally not ready
to start, the available compressor will
be started.
Note: The following description
assumes compressor 1 is the down
stream compressor.
Fixed Sequence – Compressor 1/
Compressor 2 (Default mode)
If the chiller is in the Auto mode and
all interlocks have been satisfied,
compressor 1 will be started based
on the leaving water temperature
rising above the “Differential to Start”
setting. Compressors 2 will stage on
when the overall chiller average
capacity exceeds Stage ON Load
point for 30 seconds. The stage on
load point is adjustable (via service
tool) up to 50%. The default is 40%
which means that a single
compressor would have to load to
80% (the average would be 40%)
before the second compressor starts.
Both compressors will run until
chiller average capacity drops below
Stage off Load point for 30 seconds.
The Stage OFF load point is also
adjustable (via service tool) (default =
30%, range from 0 to 50%).
Compressor 2 will be shut down and
compressor 1 will run until water
temperature drops below the
differential to stop. Before shutting
down, compressor 2 will be
unloaded and compressor 1 will be
loaded to maintain the same average
capacity command.
When running chilled water
temperature at selected conditions,
the downstream compressor usually
will be the most efficient compressor
to operate at part load because
compressors on Duplex chillers are
not sized exactly the same.
Figure 12. CDHF/G sequence of operation: lead 1/lag 2

CDHF-SVU01C-EN
18
General
Information
Fixed Sequence – Compressor 2 /
Compressor 1
If the chiller is in the Auto mode and
all interlocks have been satisfied,
compressor 2 will be started based
on the leaving water temperature
rising above the “Differential to Start”
setting. Compressors 1 will stage on
when the overall chiller average
capacity exceeds Stage on Load
point for 30 seconds. The stage on
load point is adjustable up to 50%.
The default is 40% which means that
a single compressor would have to
load to 80% (the average would be
40%) before the second compressor
starts. Both compressors will run
until chiller average capacity drops
below Stage off Load point for 30
seconds. The stage off load point is
also adjustable. Compressor 1 will
be shut down and compressor 2 will
run until water temperature drops
below the differential to stop. Before
shutting down, compressor 1 will be
unloaded and compressor 2 will be
loaded to maintain the same average
capacity command.
If chilled water reset is used, the
upstream compressor usually will be
the most efficient compressor to
operate at part load. If the leaving
water temperature is reset and the
chiller only needs one compressor,
then the upstream compressor
would be running closer to its
selection point and will be the most
efficient compressor to operate.
Figure 13. CDHE/F/G sequence of operation: lead 2 lag 1

19
CDHF-SVU01C-EN
General
Information
Sequencing - Balanced Starts and
Hours
When desired to balance the wear
between the compressors. This
method will extend the time between
maintenance on the lead compressor.
When balanced starts and hours is
selected, the compressor with the
fewest starts will start. If that
compressor is unavailable to start
due to a circuit lockout (including
restart inhibit) or a circuit diagnostic,
then the other compressor will be
started. The second compressor will
stage on when chiller capacity
exceeds the Stage on Load point for
30 seconds. When chiller capacity
falls below Stage off Load point for
30 seconds, the compressor with the
most hours will be shut off.
Figure 14. CDHF/G sequence of operation: equalize starts and hours

CDHF-SVU01C-EN
20
General
Information
Simultaneous Compressor Start/
Stop
Both compressors will start in close
succession to minimize the time it
takes for the chiller to reach full load.
Some process applications need the
chiller to start and generate capacity
as fast as possible. This method will
start both compressors, slightly
staggered to prevent doubling of the
current inrush, but will generally
control the chiller as if there were
only one compressor.
If the chiller is in the Auto mode and
all interlocks have been satisfied,
compressor 1 will be started based
on the leaving water temperature
rising above the “Differential to Start”
setting. When compressor 1 is at
speed, compressor 2 will start. Both
compressors will run until water
temperature falls below the
differential to stop, at that time both
compressors will be shut down.
Figure 15. CDHF/G sequence of operation: combined start