Emerson ZR16-29KC, ZR16-24K4, ZR16-34KA, ZR38-54KA, ZR18-48K3 Application Engineering Bulletin

AE4-1312 R2

AE4-1312 R2

Application Guidelines for 1.5 to 6.75 Ton Refrigerant

R-22, 407C, 134A Copeland Scroll

Introduction

The ZR*KA, ZR*KC, ZR*K3, & ZR*K4 Copeland Scroll®
compressors include a wide range of capacities,
electrical options, and features. Typical model numbers
are ZR24K4-PFV and ZR81KC-TF5. This bulletin
describes the operating characteristics, design features,
and application requirements for these models. For
additional information, please refer to the online
product information accessible from the Emerson
Climate Technologies website at www.emersonclimate.
com. Operating principles of the Copeland Scroll are
described in Figure 7 at the end of this bulletin.

The ZR*KA scroll compressors are designed for air
conditioning systems only in the 12+ SEER range
but may be applied to 10 SEER A/C systems if desired.
They range in size from 16,000 to 54000 Btu/hr (4.7 to

15.8 kw-hr).

The ZR*K3 and K4 are models designed for 11+ SEER
A/C and heat pump usage ranging in size from 16,000
to 61,000 Btu/hr (4.7 to 17.9 kw-hr).

The ZR*KC models are designed for 10 SEER
A/C and heat pump usage ranging in size from 16,000
to 81,000 Btu/hr (4.7 to 23.7 kw-hr).

The models include a number of features outlined in
the matrix below:

January, 2005

Reformatted November 2010

®

Compressors

IPR Valve-Internal Pressure Relief Valve

The internal pressure relief valve is located between
the high side and the low side of the compressor. It
is designed to open when the discharge to suction
differential pressure exceeds 375 to 450 psid (26 – 32
kg/cm2). When the valve opens, hot discharge gas
is routed back into the area of the motor protector to
cause a trip.During developmental blocked fan testing,
it is sometimes noted that the valve opens, but the
compressor does not shut off while the discharge
pressure continues to climb. This condition is normally

caused by refrigerant ood back and may be corrected

by using a more restrictive expansion device or reducing
the refrigerant charge.

Internal Temperature Protection

®

The Therm-O-Disc
snap disc device located between the high and low
pressure side of the scroll. It is designed to open and
route excessively hot discharge gas back to the motor
protector. During a situation such as loss of charge,
the compressor will be protected for some time while
it trips on the protector. However, as refrigerant leaks

out, the mass ow and the amperage draw are reduced

and the scrolls will start to overheat. Normally, during
air conditioning operation the problem is detected
because of rising indoor temperatures before damage
is done. This may not be the case during heat pump

or TOD is a temperature-sensitive

Motor

Frame Size*

ZR16-29KC 53 X X NO X X X X

ZR16-24K4 53 X X NO X X X X
ZR16-34KA 53 X NO X X X X X
ZR38-54KA 63 X NO X X X X X

ZR18-48K3 63 X X X X X X X
ZR26-48KC 63 X X X X X X X

ZR54-61K3 70 X X X X X X X
ZR54-81KC 70 X X X X X X X

* Approximate Shell Diameter (e.g. 53 = 5.5 Inches)

© 2010 Emerson Climate Technologies
Printed in the U.S.A.

Application

AC HP

IPR TOD

1

Quiet Shut

Down

Discharge

Check Valve

Motor

Protector

AE4-1312 R2

operation since backup heat will make up the decit. A

low pressure control is recommended for loss of charge
protection in heat pumps for the highest level of system
protection. A cut out setting no lower than 25 psig (2
kg/cm2) for air conditioning and 7 psig (0.5 kg/cm2) for
heat pumps is recommended. The low pressure cut-out,
if installed in the suction line to the compressor, can
provide additional protection against a TXV failed in the
closed position, outdoor fan failure in heating, a closed
liquid line or suction line service valve, or a blocked liquid

line screen, lter, orice, or TXV. All of these can starve

the compressor for refrigerant and result in compressor
failure. The low pressure cut-out should have a manual
reset feature for the highest level of system protection. If
a compressor is allowed to cycle after a fault is detected,
there is a high probability that the compressor will be
damaged and the system contaminated with debris from
the failed compressor and decomposed oil. If current
monitoring to the compressor is available, the system
controller can take advantage of the compressor TOD
and internal protector operation. The controller can lock
out the compressor if current draw is not coincident with
the contactor energizing, implying that the compressor
has shut off on its internal protector. This will prevent
unnecessary compressor cycling on a fault condition
until corrective action can be taken.

Quiet Shut down

All scrolls in this size range have one of several
types of “quiet” shutdown solutions. The ZR..KC/K3/
K4 Scrolls up to four tons use a cam-type device that
separates the scrolls when they are driven backwards
as high-pressure gas equalizes from the high side
of the compressor to the low side during shutdown.
Larger scrolls with 70 frame motors through ZR61 use
a different type of cam that stops backward rotation
during shut down. Models ZR68KC through ZR81KC

will continue to be built with the uid brake design,

so a momentary reverse rotation sound will be heard
from these compressors. The newer ZR..KA scrolls
incorporate a non dynamic discharge port check valve
that prevents high pressure gas trapped in the dome
from returning through the scroll set. All of these quiet
shut down solutions allow the scroll compressor to
restart immediately even if the system is not equalized
eliminating the need for a time delay. Development
testing should include a review of the shutdown sound
for acceptability in a particular system. Also refer to
section on “Brief Power Interruption”.

Discharge Check Valve

A low mass, disc-type check valve in the discharge tting

of the compressor prevents the high side, high pressure

discharge gas from owing rapidly back through the

compressor. This check valve was not designed to be

used with recycling pump down because it is not entirely
leak-proof.

Motor Protector

Conventional internal line break motor protection is
provided. The protector opens the common connection
of a single-phase motor and the center of the Y
connection on three-phase motors. The three-phase
protector provides primary single-phase protection. Both
types of protectors react to current and motor winding
temperature.

Field Replacement of obsolete Single Phase ZR*K1
or ZR*K2 with Equivalent Capacity ZR*K3/K4/KA/
KC, Scroll Compressors

The discharge and suction tting sizes as well as the
mounting foot pattern of the new models are identical
to the ZR*K1 or ZR*K2. Tubing location is identical in

most cases for easy eld replacement. The ZR*K1

has an external top cap thermostat to limit discharge
temperature. This feature has been replaced by the
Therm-O-Disc® located inside the new scrolls. When
replacing the ZR*K1, the top cap thermostat wires
must be removed and the control circuit wires spliced
together. See section on Compressor Replacement

after Motor Burn for further tips on eld replacement.

The replacement compressor will need a new run
capacitor if the old capacitor is more than 5 microfarads
different or the voltage rating of the old capacitor is
lower than the new one. See compressor nameplate
or Table 4 for recommended run capacitor. Note that
the ZR*KA may only be used to replace compressors
used for A/C, not heat pumps.

Application Considerations

The Copeland Scroll compressor has a number of
application characteristics that are different from those
of the traditional reciprocating compressor. These are
detailed below.

Accumulators

The use of accumulators is very dependent on the
application. The Copeland Scroll’s inherent ability to
handle liquid refrigerant during occasional operating

ood back situations make the use of an accumulator

unnecessary in standard designs such as condensing

units. Applications, such as heat pumps with orice

refrigerant control, that allow large volumes of liquid

refrigerant to ood back to the compressor during

normal steady operation can dilute the oil to such an
extent that bearings are inadequately lubricated and
wear will occur. In such a case an accumulator must

be used to reduce ood back to a safe level that the
compressor can handle. To test for ood back conditions

© 2010 Emerson Climate Technologies
Printed in the U.S.A.

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AE4-1312 R2

and determine if the accumulator design is adequate,
please see the section entitled Excessive Liquid Flood
back Tests at the end of this bulletin. The accumulator

oil return orice should be from .040 to .055 inches (1 –

1.4 mm) in diameter depending on compressor size and

compressor ood back results. A large-area protective
screen no ner than 30 x 30 mesh (0.6 mm openings)
is required to protect this small orice from plugging.
Tests have shown that a small screen with a ne mesh

can easily become plugged causing oil starvation to the
compressor bearings.

Screens

The use of screens ner than 30 x 30 mesh (0.6mm

openings) anywhere in the system should not be
used with these compressors. Field experience has

shown that ner mesh screens used to protect thermal

expansion valves, capillary tubes, or accumulators
can become temporarily or permanently plugged with

normal system debris and block the ow of either oil or

refrigerant to the compressor. Such blockage can result
in compressor failure.

Crankcase Heat - Single Phase

Crankcase heaters are not required on single phase
compressors when the system charge is not over the
120% limit shown in Table 5. A crankcase heater is
required for systems containing more than 120% of the
compressor refrigerant charge limit listed in Table 5.
This includes long line length systems where the extra
charge will increase the standard factory charge above
the 120% limit.

Experience has shown that compressors may ll with

liquid refrigerant under certain circumstances and

system congurations, notably after longer off cycles

when the compressor has cooled. This may cause
excessive start up clearing noise or the compressor
may lock up and trip on protector several times before
starting. The addition of a crankcase heater will reduce
customer noise and dimming light complaints since the
compressor will no longer have to clear out liquid during
start. Table 6 lists the crankcase heaters recommended
for the various models and voltages.

Crankcase Heat – Three-Phase

A crankcase heater is required for three-phase
compressors when the system charge exceeds the
compressor charge limit listed in Table 5 and an
accumulator cannot be piped to provide free liquid
drainage during the off cycle (See Figure 2 and Table

6).

Pump down Cycle

A pump down cycle for control of refrigerant migration
is not recommended for scroll compressors of this size.

If a pump down cycle is used, a separate external
check valve must be added. The scroll discharge

check valve is designed to stop extended reverse
rotation and prevent high-pressure gas from leaking
rapidly into the low side after shut off. The check
valve will in some cases leak more than reciprocating
compressor discharge reeds, normally used with pump
down, causing the scroll compressor to recycle more
frequently. Repeated short-cycling of this nature can
result in a low oil situation and consequent damage to
the compressor. The low-pressure control differential
has to be reviewed since a relatively large volume of
gas will re-expand from the high side of the compressor
into the low side on shut down.

Minimum Run Time

There is no set answer to how often scroll compressors
can be started and stopped in an hour, since it is
highly dependent on system configuration. Other
than the considerations in the section on Brief Power
Interruptions, there is no minimum off time because
scroll compressors start unloaded, even if the
system has unbalanced pressures. The most critical
consideration is the minimum run time required
to return oil to the compressor after startup. To
establish the minimum run time obtain a sample
compressor equipped with a sight tube (available from
Emerson Climate Technologies) and install it in a system
with the longest connecting lines that are approved for
the system. The minimum on time becomes the time
required for oil lost during compressor startup to return
to the compressor sump and restore a minimal oil
level that will assure oil pick up through the crankshaft.
Cycling the compressor for a shorter period than this,
for instance to maintain very tight temperature control,
will result in progressive loss of oil and damage to the
compressor. See Application Engineering Bulletin 17­1262 for more information on preventing compressor
short cycling.

Reversing Valves

Since Copeland Scroll compressors have very high

volumetric efciency, their displacements are lower

than those of comparable capacity reciprocating
compressors. As a result, Emerson recommends that
the capacity rating on reversing valves be no more than
2 times the nominal capacity of the compressor with
which it will be used in order to ensure proper operation
of the reversing valve under all operating conditions.

© 2010 Emerson Climate Technologies
Printed in the U.S.A.

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AE4-1312 R2

The reversing valve solenoid should be wired so that the
valve does not reverse when the system is shut off by
the operating thermostat in the heating or cooling mode.
If the valve is allowed to reverse at system shutoff,
suction and discharge pressures are reversed to the
compressor. This results in pressures equalizing through
the compressor which can cause the compressor to
slowly rotate until the pressures equalize. This condition
does not affect compressor durability but can cause
unexpected sound after the compressor is turned off.

Low Ambient Cut-Out

A low ambient cut-out is not required to limit air-to-air
heat pump operation. Air-to-water heat pumps must

be reviewed since this conguration could possibly run

outside of the approved operating envelope (Figure 5)
causing overheating or excessive wear.

Oil Type

Several types of compatible mineral oils are used in
the R-22 compressors. A standard 3GS oil may be

used if the addition of oil in the eld is required. See

the compressor nameplate for original oil charge. See
Application Engineering bulletin 17-1248 for more
information about oil types Emerson uses. A complete

recharge should be four uid ounces (118 ml) less than

the nameplate value. Some models have been released
for use with R407C or 134a and use polyol ester oil,

identied as POE, along with the charge quantity on

the nameplate. These models have an “E” in the 7th
place of the model number. An example would be the
ZR24K3E-PFJ compressor. Copeland® Ultra 22 CC

should be used if additional oil is needed in the eld.

Mobil Arctic EAL22CC or ICI Emkarate RL32CF oil may
be used to recharge these compressors if Ultra 22 is
not available. Compressors charged with POE may be
used with R-22 but compressors charged with mineral
oil may not be used with HFC refrigerants such as 407C
or 134a because they are not miscible.

Discharge Mufers

Flow through Copeland Scroll compressors is semi­continuous with relatively low pulsation. External

mufers, where they are normally applied to piston

compressors today, may not be required for Copeland
Scroll. Because of variability between systems, however,
individual system tests should be performed to verify
acceptability of sound performance. When no testing is

performed, mufers are recommended in heat pumps.
A hollow shell mufer such as the Alco APD-1 or APD-
054 will work quite well. The mufer should be located

a minimum of six inches (15 cm) to a maximum of 18
inches (46 cm) from the compressor for most effective

operation. The further the mufer is placed from the

compressor within these ranges the more effective it
may be. If adequate attenuation is not achieved, use a

mufer with a larger cross-sectional area to inlet-area

ratio. The ratio should be a minimum of 20 to 1 with a

30 to 1 ratio recommended. The mufer should be from

four to six inches (10-15 cm) long.

Air Conditioning System Suction Line Noise and
Vibration

Copeland Scroll compressors inherently have low sound
and vibration characteristics. However, the sound and
vibration characteristics differ in some respects from
those of reciprocating compressors. In rare instances,
these could result in unexpected sound complaints.

One difference is that the vibration characteristic of
the scroll compressor, although low, includes two very
close frequencies, one of which is normally isolated
from the shell by the suspension of an internally
suspended compressor. These frequencies, which
are present in all compressors, may result in a low
level “beat” frequency that may be detected as noise
coming along the suction line into a house under some
conditions. Elimination of the “beat” can be achieved
by attenuating either of the contributing frequencies.
The most important frequencies to avoid are line and
twice-line frequencies for single-phase compressors
and line frequency for three phase compressors. This is
easily done by using one of the common combinations
of design congurations described in Table 3. The scroll
compressor makes both a rocking and torsional motion,

and enough exibility must be provided in the line to

prevent vibration transmission into any lines attached to
the unit. In a split system the most important goal is to
ensure minimal vibration in all directions at the service
valve to avoid transmitting vibrations to the structure to
which the lines are fastened.

A second difference of the Copeland Scroll is that
under some conditions the normal rotational starting
motion of the compressor can transmit an “impact”
noise along the suction line. This may be particularly
pronounced in three-phase models due to their
inherently higher starting torque. This phenomenon,
like the one described previously, also results from the
lack of internal suspension, and can be easily avoided
by using standard suction line isolation techniques as
described in Table 3.

The sound phenomena described above are not usually
associated with heat pump systems because of the
isolation and attenuation provided by the reversing valve
and tubing bends.

© 2010 Emerson Climate Technologies
Printed in the U.S.A.

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AE4-1312 R2

Single Phase Starting Characteristics

Start assist devices are usually not required, even if
a system utilizes non-bleed expansion valves. Due to
the inherent design of the Copeland Scroll, the internal
compression components always start unloaded even
if system pressures are not balanced. In addition, since
internal compressor pressures are always balanced at
startup, low voltage starting characteristics are excellent
for Copeland Scroll compressors. Starting current on

any compressor may result in a signicant “sag” in

voltage where a poor power supply is encountered. The
low starting voltage reduces the starting torque of the
compressor and subsequently increases the start time.
This could cause light dimming or a buzzing noise where
wire is pulled through conduit. The start components
listed in Table 7 will substantially reduce start time and
consequently the magnitude and duration of both light
dimming and conduit buzzing.

PTC Start Components

For less severe voltage drops or as a start boost, solid

state Positive Temperature Coefcient devices rated

from 10 to 25 ohms may be used to facilitate starting
for any of these compressors.

Electrical Connection

The orientation of the electrical connections on the
Copeland Scroll compressors is shown in Figure 4.
Three electrical connection options are available for
these compressors. These include the “Molded Plug”
one piece push-on connection, available in certain

markets, and “Quick Connect” ag termination available

on all scrolls of this size. Some four-ton and larger
models also offer “T-block Screw Connection” for ring
termination.

Deep Vacuum Operation

Scrolls incorporate internal low vacuum protection
and will stop pumping (unload) when the pressure
ratio exceeds approximately 10:1. There is an audible
increase in sound when the scrolls start unloading.

Copeland Scroll compressors (as with any refrigerant
compressor) should never be used to evacuate a
refrigeration or air conditioning system. The scroll
compressor can be used to pump down refrigerant in a
unit as long as the pressures remain within the operating
envelope shown in Figure 5. Prolonged operation at
low suction pressures will result in overheating of the
scrolls and permanent damage to the scroll tips, drive
bearings and internal seal. (See AE24-1105 for proper
system evacuation procedures.)

Nomenclature

The model numbers of the Copeland Scroll compressors
include the approximate nominal 60 HZ capacity at
standard operating conditions. An example would be the
ZR24K3-TFD, which has 24,500 Btu/hr (7 kw) cooling
capacity at the ARI high temperature air conditioning
rating point when operated on 60 Hz. Note that the
same compressor will have approximately 5/6 of this
capacity or 20,200 Btu/hr (5.9 kw) when operated on 50
Hz current. Please refer to Online Product Information
at www.emersonclimate.com for details.

Shell Temperature

Certain types of system failures, such as condenser
or evaporator fan blockage or loss of charge, may

cause the top shell and discharge line to briey but

repeatedly reach temperatures above 350ºF (177ºC)
as the compressor cycles on its internal protection
devices. Care must be taken to ensure that wiring or
other materials, which could be damaged by these
temperatures, do not come in contact with these
potentially hot areas.

Suction and Discharge Fittings

Copeland Scroll compressors have copper plated steel

suction and discharge ttings. These ttings are far
more rugged and less prone to leaks than copper ttings

used on other compressors. Due to the different thermal
properties of steel and copper, brazing procedures may
have to be changed from those commonly used. See

Figure 6 for assembly line and eld brazing procedures.

Three Phase Scroll Compressors

Scroll compressors, like several other types of
compressors, will only compress in one rotational
direction. Direction of rotation is not an issue with
single phase compressors since they will always start
and run in the proper direction (except as described in
the section “Brief Power Interruptions”). Three phase
compressors will rotate in either direction depending
upon phasing of the power. Since there is a 50-50
chance of connecting power in such a way as to cause
rotation in the reverse direction, it is important to

include notices and instructions in appropriate
locations on the equipment to ensure proper
rotation direction is achieved when the system
is installed and operated. Verification of proper

rotation direction is made by observing that suction
pressure drops and discharge pressure rises when the
compressor is energized. Reverse rotation will result
in substantially-reduced current draw compared to
normal values.

© 2010 Emerson Climate Technologies
Printed in the U.S.A.

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AE4-1312 R2

There is no negative impact on durability caused by
operating three phase Copeland Scroll compressors in
the reversed direction for a short period of time (under
one hour) but oil may be lost. After several minutes of
reverse operation, the compressor’s internal protector
will trip. If allowed to repeatedly restart and run in
reverse without correcting the situation, the compressor
will be permanently damaged because of oil loss to
the system. Oil loss can be prevented during reverse
rotation if the tubing is routed at least six inches (15
cm) above the compressor. All three-phase scroll
compressors are wired identically internally. As a result,

once the correct phasing is determined for a specic

system or installation, connecting properly phased

power leads to the identied compressor electrical

(Fusite) terminals will maintain proper rotation direction.
See Fig 4. It should be noted that all three phase scrolls
will continue to run in reverse until the protector opens
or the phasing is corrected.

Brief Power Interruptions

Brief power interruptions (less than 1/2 second) may
result in powered reverse rotation of single-phase
Copeland Scroll compressors. This occurs because
high-pressure discharge gas expands backward through
the scrolls during power interruption, causing the scroll
to orbit in the reverse direction. When power is reapplied
while reverse rotation is occurring, the compressor may
continue to run in the reverse direction for some time
before the compressor’s internal protector trips. This
has no effect on durability. When the protector resets,
the compressor will start and run normally.

To avoid disruption of operation, an electronic control
that can sense brief power interruptions may be used
to lock out the compressor for a short time. This control
could be incorporated in other system controls (such
as defrost or thermostat), or be a stand-alone control.

Functional specications for this control as well as a

suggested wiring diagram are shown in Figure 3.

Because three-phase models have high enough torque
to prevent reverse rotation after power interruptions no
time delay is necessary.

ASSEMBLY LINE PROCEDURES

Installing the compressor

Scroll compressors leave the factory dehydrated with
a positive dry air charge. Plugs should not be removed
from the compressor until the compressor has had

sufcient time to warm up if stored outside and is ready

for assembly to the unit. It is suggested that the larger

suction plug be removed rst to relieve the internal

pressure. Removing the smaller discharge plug could

result in a spray of oil out of this tting since some oil

would accumulate in the head of the compressor after
Emerson test runs the compressor. The inside of both

ttings should we wiped with a lint free wipe to remove

residual oil prior to brazing. A compressor containing
mineral oil should never be left open longer than 15
minutes or 5 minutes if it contains POE oil.

Assembly Line Brazing Procedure
Figure 6 discusses the proper procedures for brazing

the suction and discharge lines to a scroll compressor.

It is important to ow nitrogen through the system

while brazing all joints during the system assembly
process. Nitrogen displaces the air and prevents the

formation of copper oxides in the system. If allowed

to form, the copper oxide akes can later be swept

through the system and block screens such as those
protecting capillary tubes, thermal expansion valves,
and accumulator oil return holes. The resulting
blockage of oil or refrigerant may do damage resulting
in compressor failure.

Pressure Testing

The pressure used on the line to meet the UL burst
pressure requirement can not be higher than 400 psig.
Higher pressure might result in permanent deformation
of the compressor shell and possibly cause rotor slip.

Assembly Line System Charging Procedure

Systems should be charged on both the high and low
sides simultaneously. The majority of the charge should
be placed in the high side of the system to prevent low

volt start difculties, Hipot failures, and bearing washout
during rst-time start on the assembly line. It is best to

charge only vapor into the low side of the system. Do
not operate compressor without enough system
charge to maintain at least 7 psig (0.5kg/cm2)
suction pressure. Do not operate with a restricted
suction. Do not operate with the low pressure cut­out disabled. Allowing pressure to drop below 7 psig

(0.5 kg/cm2) for more than a few seconds may overheat
scrolls and cause early drive bearing damage. Do not
use compressor to test opening set point of a high
pressure cutout. Bearings are susceptible to damage
before they have had several hours of normal running
for proper break in.

“Hipot” (AC High Potential) Testing

Copeland Scroll compressors are congured with the

motor down and the pumping components at the top
of the shell. As a result, the motor can be immersed
in refrigerant to a greater extent than hermetic
reciprocating compressors when liquid refrigerant is
present in the shell. In this respect, the scroll is more like

© 2010 Emerson Climate Technologies
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