Danfoss Maneurop NTZ Series Instruction Manual

MAKING MODERN LIVING POSSIBLE
SELECTION & APPLICATION
GUIDELINES
Maneurop® reciprocating compressors
NTZ
R404A - R507A

MANEUROP® RECIPROCATING COMPRESSORS ........................................................................................................... 4
Features ................................................................................................................................................................................................................................................................... 4
Compressor reference ............................................................................................................................................................................................................. 4
INTRODUCTION ............................................................................................................................................................................................................................................. 5
Code numbers .......................................................................................................................................................................................................................................... 5
Packaging ............................................................................................................................................................................................................................................................ 5
SPECIFICATIONS .......................................................................................................................................................................................................................................... 6
Technical specications and nominal ratings ...................................................................................................................... 6
Approvals and certicates ............................................................................................................................................................................................... 6
Operating envelope ..................................................................................................................................................................................................................... 6
OUTLINE DRAWINGS .......................................................................................................................................................................................................................... 7
1 cylinder ............................................................................................................................................................................................................................................................. 7
2 cylinders .......................................................................................................................................................................................................................................................... 8
4 cylinders .......................................................................................................................................................................................................................................................... 9
ELECTRICAL CONNECTIONS AND WIRING ........................................................................................................................... 10
Voltage application range........................................................................................................................................................................................... 10
Electrical connections ......................................................................................................................................................................................................... 10
Single phase electrical characteristics ............................................................................................................................................ 10
Nominal capacitor values and relays ................................................................................................................................................. 11
Single phase motor protection and suggested wiring diagram ........................................... 11
Three phase electrical characteristics .................................................................................................................................................. 13
Three phase motor protection and suggested wiring diagram ................................................. 13
REFRIGERANTS AND LUBRICANTS .............................................................................................................................................................. 15
SYSTEM DESIGN RECOMMENDATIONS ............................................................................................................................................ 16
Piping design .............................................................................................................................................................................................................................................. 16
Operating limits .................................................................................................................................................................................................................................... 18
Motor protection ............................................................................................................................................................................................................................... 19
Discharge temperature protection ............................................................................................................................................................ 19
Liquid refrigerant control and charge limits ......................................................................................................................... 20
SOUND AND VIBRATION MANAGEMENT .................................................................................................................................... 22
Sound .......................................................................................................................................................................................................................................................................... 22
Vibration ............................................................................................................................................................................................................................................................... 22
INSTALLATION AND SERVICE .................................................................................................................................................................................... 23
System cleanliness .......................................................................................................................................................................................................................... 23
Compressor handling, mounting and connection .................................................................................................. 23
System pressure test .................................................................................................................................................................................................................. 24
Leak detection ......................................................................................................................................................................................................................................... 25
Vacuum pump-down and dehydration procedure ................................................................................................ 25
Start-up ................................................................................................................................................................................................................................................................... 25
CONTENTS

NT Z 4 L048 A R1 A
4: Motor voltage code
(see table page 4)
R1: Equipment version
(R1: Rotolock connections,
oil equalisation connection
and sight glass)
L: Motor protection
(L: Internal Motor Protection)
NT: New low
temperature
reciprocating
compressors
A: Evolution index,
indicating
compressor
modications
Z: Polyolester lubricant
048: Displacement in cm3/ rev.
A: UL index indicator
4
MANEUROP® RECIPROCATING COMPRESSORS
Features The Maneurop® NTZ series from
Danfoss Commercial Compressors
is a range of hermetic reciprocating
compressors for low evaporating tem-
perature applications. These compres-
sors gradually replace the existing LTZ
range.
The NTZ series is engineered as a true
low temperature compressor, opti-
mised at –35°C with an extended
evaporating temperature range from
–45°C up to –10°C. The compressors
can be operated at a return gas tem-
perature (suction gas temperature)
of 20°C even at low evaporating
temperatures.
A liquid injection system is not re-
quired. All components are of high
quality and precision to assure a long
product life.
NTZ compressors have a large internal
free volume that helps to reduce the
risk of liquid hammering. The electri-
cal motor is fully suction gas cooled
which means that no additional body
cooling is required and it allows the
compressor to be insulated with an
acoustic hood when the installation
requirements call for extra low sound
characteristics.
Compressor reference
(indicated on the compressor
nameplate)

5
INTRODUCTION
Code numbers
(for ordering)
The code numbers for NTZ compres-
sors are according to the standard
Danfoss numbering system. Below
tables list the code numbers for NTZ
compressors in single packs and
industrial packs.
* Single pack: one compressor packed in a cardboard box 4 cyl.: cardboard box on 1/4 euro pallet
** Multi pack: a pallet lled with single-packs
*** Industrial pack: a full pallet of unpacked compressors
Packaging
NTZ compressors in single pack*
NTZ compressors in industrial pack***
Compressor
model
Code no.
Motor voltage code
13459
Nominal voltage
208-230/1/60 200-230/3/60 460/3/60
400/3/50 230/1/50 380/3/60
NTZ048 120F0072 120F0026 120F0001 120F0087 120F0168
NTZ068 120F0073 120F0027 120F0002 120F0088 120F0169
NTZ096 120F0074 120F0028 120F0003
NTZ108 120F0075 120F0029 120F0004 120F0170
NTZ136 120F0076 120F0030 120F0005 120F0171
NTZ215 120F0031 120F0006 120F0172
NTZ271 120F0032 120F0007 120F0173
NTZ430 120F0024
NTZ542 120F0025
Compressor
model
Code no.
Motor voltage code
13459
Nominal voltage
208-230/1/60 200-230/3/60 460/3/60
400/3/50 230/1/50 380/3/60
NTZ048 120F0077 120F0033 120F0008 120F0089 120F0174
NTZ068 120F0078 120F0034 120F0009 120F0090 120F0175
NTZ096 120F0079 120F0035 120F0010
NTZ108 120F0080 120F0036 120F0011 120F0176
NTZ136 120F0081 120F0037 120F0012 120F0177
NTZ215 120F0038 120F0013 120F0178
NTZ271 120F0039 120F0014 120F0179
Compressor
model
Single pack* Multi pack ** Industrial pack***
Net weight
(kg)
Dimensions
(mm) Qty Net weight (kg)
Dimensions
(mm)
Static
stacking Qty Net weight (kg)
Dimensions
(mm)
Static
stacking
NTZ048 21 l: 385
w: 285
h: 370
8
178 l: 1150
w: 800
h: 510
4
12
244 l: 1150
w: 800
h: 500
4
NTZ068 23 194 268
NTZ096 35
l: 385
w: 375
h: 450
6
220
l: 1150
w: 800
h: 600
6
208
l: 1150
w: 800
h: 600
NTZ108 35 220 208
NTZ136 35 220 208
NTZ215 62 l: 570
w: 400
h: 670
4
382 l: 1150
w: 800
h: 820
6
364 l: 1150
w: 800
h: 710
NTZ271 64 394 376
tandem units

6
Compressor
model Swept
volume
cm3/rev
Displacement Nominal ratings*
Number
of
cylinders
Oil
charge
litre
Net
weight
kg
50 Hz
2900 rpm
m3/hr
60 Hz
3500 rpm
m3/hr
50 Hz 60 Hz
Cooling
capacity
W
COP
W/W
Cooling
capacity
W
COP
W/W
NTZ048 48 8.4 10.1 995 1.15 1190 1.13 1 0.95 21
NTZ068 68 11.8 14.3 1749 1.15 1870 1.10 1 0.95 23
NTZ096 96 16.7 20.2 2002 1.15 2395 1.16 2 1.8 35
NTZ108 108 18.7 22.6 2465 1.16 2788 1.10 2 1.8 35
NTZ136 136 23.6 28.5 3225 1.11 3739 1.12 2 1.8 35
NTZ215 215 37.5 45.2 4948 1.19 5886 1.19 4 3.9 62
NTZ271 271 47.3 57.0 6955 1.24 8058 1.21 4 3.9 64
SPECIFICATIONS
Technical specications and nominal ratings
Operating envelope
R404A / R507A
(*) Motor code 4 operating conditions: R404A, Evap. temp.: -35°C, Cond. temp.: 40°C, RGT: 20°C, SC: 0K
For full NTZ data details and capacity tables refer to Online Datasheet Generator: www.danfoss.com/odsg
Approvals and certicates Maneurop® NTZ compressors comply
with the following approvals and cer-
ticates.
Certicates are listed on the product
datasheets:
http://www.danfoss.com/odsg
Versions Available equipment version:
R1: Rotolock suction and discharge
connections, 3/8" are oil equalisation
connection, threaded sight glass.
CE
(European Directive) All models
UL
(Underwriters Laboratories)
Models with motor voltage code 1, 3 & 4
NTZ048 - 9 & NTZ068-9
CCC (China Compulsory
Product Certication) Models with motor voltage code 4 & 5.
Gost
certicate (for Russia) Models with motor voltage code 4 & 5.

Oil equalisation
3/8”
PTC crankcase heater
25
98
Schrader
1/4”
26
3
333
Suction rotolock
1”1/4
Discharge rotolock
1”
68
82
109 118
35° 33°
68
Suction 147
Discharge 142
159
17
17°
123
39
Threaded oil
sight glass
141
ø 224
68
HM8-40
23
15
Silent block
7
1 cylinder
OUTLINE DRAWINGS
Rotolock connections size Pipe sizing Rotolock valve
Suction Discharge Suction Discharge Suction Discharge
NTZ048
NTZ068 1”1/4 1” 5/8” 1/2” V09 V06

98
60 156
8
Suction 179
Discharge 176
252
ø 288
413
32
Threaded oil
sight glass
Schrader
1/4"
PTC
crankcase heater
96
21
145
125
188
171
8
38
82
74 68
265
Suction rotolock
1"3/4
Discharge rotolock
1"1/4
Oil equalisation
3/8"
HM8-40
23
15
Silent block
8
OUTLINE DRAWINGS
2 cylinders
Rotolock connections size Pipe sizing Rotolock valve
Suction Discharge Suction Discharge Suction Discharge
NTZ096
NTZ108 1”3/4 1”1/4 7/8” 3/4” V07 V04
NTZ136 1”3/4 1”1/4 1"1/8” 3/4” V02 V04

4 cylinders
99
158
232
202
246
205
246
115
ø 352
95
125
233
519
15
96
15
15
Threaded oil
sight glass
Schrader
1/4"
Mounting hole for PTC
crankcase heater
Suction rotolock
1"3/4
Discharge rotolock
1"1/4
Oil equalisation
3/8" (VE version only)
Rotolock connections size Pipe sizing Rotolock valve
Suction Discharge Suction Discharge Suction Discharge
NTZ215
NTZ271 1”3/4 1”1/4 1"1/8” 3/4” V02 V04
30
19
HM12-50
Silent block
9
OUTLINE DRAWINGS

10
Voltage application range
ELECTRICAL CONNECTIONS AND WIRING
Electrical connections
Motor voltage code Nominal voltage Voltage application range
1 208-230 V / 1 / 60 Hz 187 – 253 V
3 200-230 V / 3 / 60 Hz 180 – 253 V
4380-400 V / 3 / 50 Hz
460 V / 3 / 60 Hz
340 – 440 V (50 Hz)
414 – 506 V (60Hz)
5 230 V / 1 / 50 Hz 207 – 253 V
9 380 V / 3 / 60 Hz 342 – 418 V
Models: NTZ215 - NTZ271 - NTZ136-1
IP rating: 54 (with cable gland)
Screw
10-32 UNF x 9,5
Earth M4-12
Knock-out
Ø 29 mm
Ø 29 mm
Models: NTZ048 - NTZ068 - NTZ096 - NTZ108 - NTZ136 (except NTZ136-1)
Spade connectors
1/4” AMP-AWE
Earth M4-12
Knock-out
Ø 21 mm
Ø 21 mm
IP rating: 55 (with cable gland)
LRA - Locked Rotor
Current (A)
MCC - Maximum
Continuous Current (A)
Winding resistance (Ω)
( ± 7 % at 20° C)
Motor Code 1515 1 5
Winding run start run start
NTZ048 43.7 37 13.2 11 1.32 4.16 1.62 3.95
NTZ068 72 53 21 17 0.94 2.01 1.05 3.19
NTZ096 97 31 0.45 1.84
NTZ108 97 33 0.45 1.84
NTZ136 140 41 0.36 1.73
Single phase electrical
characteristics

11
50 Hz PSC/CSR* CSR only
Models
Run
capacitors (1)
Start
capacitors (2) Start
relay
(A) μF (C) μF (B) μF
NTZ048 20 10 100 3ARR3J4A4
NTZ068 20 10 100
60 Hz PSC/CSR* CSR only
Models
Run
capacitors (1)
Start
capacitors (2) Start
relay
(A) μF (C) μF (B) μF
NTZ048 15 10 100
3ARR3J4A4
NTZ068 25 25 135
NTZ096 30 15 135
NTZ108 30 15 135
NTZ136 30 15 135
ELECTRICAL CONNECTIONS AND WIRING
Nominal capacitor values
and relays
* PSC: Permanent Split Capacitor
CSR: Capacitor Start Run
(1) Run capacitors: 440 volts
(2) Start capacitors: 330 Volts
Single phase motor
protection and suggested
wiring diagram
Single phase compressor motors are
internally protected by a temperature
/ current-sensing bimetallic protector
which senses the main and start wind-
ing current as well as motor winding
temperature. If the motor were to be
overloaded and the protector trips, it
might take up to several hours to reset
and restart the compressor.
The standard CSR wiring system pro-
vides additional motor torque at start-
up, by the use of a start capacitor in
combination with a run capacitor. The
start capacitor is only connected dur-
ing the starting operation and a poten-
tial relay disconnects it after the start
sequence. This sytem can be used for
refrigerant circuits with capillary tubes
or expansion valves.
Single phase
PSC wiring
with trickle circuit
IOL Motor protector
A & C Run capacitors
CCommon
SStart winding (auxiliary)
RRun winding (main)

12
ELECTRICAL CONNECTIONS AND WIRING
Single phase
CSR wiring
with trickle circuit
IOL Motor protector
A & C Run capacitors
BStart capacitor
CCommon
SStart winding (auxiliary)
RRun winding (main)
IOL Motor protector
A + C Run capacitors
BStart capacitor
CCommon
SStart winding (auxiliary)
RRun winding (main)
Capacitors Aand Care replaced by a single
capacitor of size A + C
Single phase
CSR wiring without trickle
circuit

PTC
FU
FU
C1
EC
TH
N
L1
L2
L3
C1
MS
IOL
Comp.
13
ELECTRICAL CONNECTIONS AND WIRING
Three phase motor
protection and
suggested wiring
diagram
Three phase compressors are inter-
nally protected by a temperature /
current-sensing bimetallic protector,
connected to the neutral point of the
star-connected stator windings. This
internal overload line break protects
the motor against overheating, cur-
rent overload and locked rotor con-
ditions. If the motor were to be over-
loaded and the protector trips, all
3-phases are cut out. It might take up
to several hours to reset and restart
the compressor.
FU Fuses
MS Main switch
C1 Compressor contactor
TH Thermostat
EC External controls
COMP Compressor
PTC Crankcase heater
IOL Internal overload line break
Three phase electrical
characteristics
Compressor
model
LRA
(Locked Rotor Amp)
A
MCC
(Maximum Continuous Current)
A
Winding resistance
(between phases +/- 7% at 25°C)
Ohm
349349349
NTZ048 32 16 22 10.1 4.8 5 2.80 11.55 13.10
NTZ068 48.5 25 29 14.8 8.4 8.5 1.58 7.11 9.70
NTZ096 72 32 20.4 10.1 1.20 5.03
NTZ108 72 45 57 21.4 12.1 11 1.20 4.00 2.54
NTZ136 97.2 51 64 29 14.3 15 0.98 3.80 2.54
NTZ215 147.7 74 110 42.3 22.3 23 0.57 2.23 1.26
NTZ271 198 96 150 56.5 27.0 30 0.41 1.61 0.84

14
Wiring diagram
without pump-down cycle
Control device ............................................................................................. TH
Optional short cycle timer (3 min) 5 pts ........ 180 s
Control relay ................................................................................................... KA
Compressor contactor .................................................................... KM
Safety lock out relay ............................................................................. KS
H.P. switch .......................................................................................................... HP
Fused disconnect .................................................................................... Q1
Fuses ............................................................................................................................ F1
External overload protection .................................................. F2
Compressor motor ................................................................................... M
Discharge gas thermostat ..................................................... DGT
ELECTRICAL CONNECTIONS AND WIRING
Wiring diagram
with pump-down cycle
Control device ............................................................................................. TH
Optional short cycle timer (3 min) 5 pts ........ 180 s
Control relay ................................................................................................... KA
Liquid Solenoid valve ................................................................. LLSV
Compressor contactor .................................................................... KM
Safety lock out relay ............................................................................. KS
Pump-down control & L.P. switch .................................... BP
H.P. switch .......................................................................................................... HP
Fused disconnect .................................................................................... Q1
Fuses ............................................................................................................................ F1
External overload protection .................................................. F2
Compressor motor ................................................................................... M
Discharge gas thermostat ..................................................... DGT
IP rating The compressor terminal boxes IP rat-
ing according to CEI 529 are:
IP55 for NTZ048 - 136
IP54 for NTZ215 - 271.
The IP ratings are only valid when cor-
rectly sized cable glands of the same IP
rating are applied.

15
REFRIGERANTS AND LUBRICANTS
Maneurop® NTZ compressors are de-
signed and optimised for refrigerants
R404A and R507A. Alternatively, refrig-
erants R407A and R407B can be used
with NTZ compressors, however these
may lead to reduced performance
characteristics and operating envelop.
The use of hydrocarbons is not author-
ised in NTZ compressors.
Only approved refrigerants and lubri-
cants as listed in below table may be
used.
Because of their thermodynamic
properties, R404A and R507A are es-
pecially suitable for low and medium
temperature applications. Danfoss
recommends the use of these refriger-
ants with NTZ compressors. Note that
R404A has a small temperature glide. It
must therefore be charged in the liquid
phase. For most other aspects howev-
er, this small glide may be neglected.
R507Aisanazeotropicmixturewithout
temperature glide.
R407A and R407B have different
thermodynamic properties than
R404A and R507A. Especially their
larger temperature glide shall not be
neglected. Using these refrigerants the
NTZ compressor capacity will be lower
than published in this document and
because of a higher discharge tem-
perature, the operating envelope will
be reduced.
*Type: HFC: Hydrouorcarbon (no chlorine component, "long-term" zero-ODP alternative)
**ODP: Ozone Depletion Potential (base R11; ODP = 1)
*** Temperature glide: dierence between saturated vapor temperature and saturated liquid
temperature at constant pressure
Refrigerant Type* ODP**
Temp.
glide***
(K)
Lubricant Remarks
R404A
HFC 0
0.7
160Z polyolester
lubricant, factory charged
(160SZ allowed
alternatively)
Recommended
R507A 0
R407A 6.6 Reduced
performance and
envelope
R407B 4.4

Maneurop® NTZ compressors have
been designed and qualied for sta-
tionary equipment using standard al-
ternating power supply. Danfoss does
not warrant the compressors for use
on mobile applications such as trucks,
railways, subways, ships etc.
These selection and application guide-
lines concern single compressors
only. For guidelines on manifolding
Maneurop® NTZ compressors, please
refer to literature called "Parallel Appli-
cation Guidelines".
16
SYSTEM DESIGN RECOMMENDATIONS
Piping design Oil in a refrigeration circuit is required
to lubricate moving parts in the com-
pressor. During normal system opera-
tion small oil quantities will continu-
ously leave the compressor, with the
discharge gas. Therefore, the system
piping shall be designed in a way
which allows a good oil circulation,
avoiding oil being trapped in the
system and ensuring a constant oil
return to the compressor. As long as
the amount of oil circulating through
the system is small it will contribute to
good system operation and improved
heat transfer eciency.
Lubricant getting trapped in the
evaporator or suction lines will aect
system performance and will ulti-
mately lead to compressor lubrication
failures. Where a poor oil return situ-
ation exists, adding lubricant will not
help safeguard the compressor. Only
a correct piping design can ensure
adequate oil circulation maintaining
safe oil level in the compressor.
Suction line Horizontal suction line sections shall
have a slope of 0.5% in the direction
of refrigerant ow (5 mm per meter).
The cross-section of horizontal suction
lines shall be such that the resulting
gas velocity is at least 4 m/s. In vertical
risers, a gas velocity of 8 to 12 m/s is
required to ensure proper oil return.
A U-trap is required at the foot of each
vertical riser. If the riser is higher than
4 m, additional U-traps are required for
each additional 4 meters.The length of
each U-trap must be as short as pos-
sible to avoid the accumulation of
excessive quantities of oil (see gure
below).

17
Discharge line Whenthecondenseris mounted above
the compressor, a loop above the con-
denser and a U-trap close to the com-
pressor are required to prevent liquid
draining from the condenser into the
discharge line during standstill.
SYSTEM DESIGN RECOMMENDATIONS
Gas velocities higher than 12 m/s will
not contribute to signicantly better
oil return. However they will cause
higher noise levels and result in higher
suction line pressure drops which will
have a negative eect on the system
capacity. Note that the suction ro-
tolock valves, which can be ordered
from Danfoss as accessories, are de-
signed for average pipe sizes, selected
for systems running at nominal condi-
tions. The pipe sizes selected for spe-
cic systems may dier from these av-
erage sizes.
The suction line must always be insu-
lated to limit suction gas superheat.
Oil charge and oil separator In most installations the initial com-
pressor oil charge will be sucient.
In installations with line runs exceed-
ing 20 m, or with many oil traps or an
oil separator, additional oil may be
required. In installations with the risk
of slow oil return such as in multiple
evaporator or multiple condenser in-
stallations, an oil separator is recom-
mended. Also refer to the section "Oil
charge and oil level".
Filter driers For new installations with NTZ com-
pressors Danfoss recommends using
the Danfoss DML 100% molecular
sieve, solid core lter drier. Molecular
sieve lter driers with loose beads from
third party suppliers shall be avoided.
For servicing of existing installations
where acid formation is present the
Danfoss DCL solid core lter driers
containing activated alumina are
recommended.
The drier is to be oversized rather than
undersized. When selecting a drier,
always take into account its capacity
(water content capacity), the system
refrigerating capacity and the system
refrigerant charge.
Suction line heat exchanger A suction line heat exchanger is
recommended for low temperature
applications, better performance and
eciency are expected. However
in hot location this may cause high
suction gas superheat which can result
in too high discharge temperature.
Suction pressure control An MOP-type expansion valve or suc-
tion pressure regulator (i.e. Danfoss
KVL) must be used to limit suction
pressure at a maximum of 4 bar rela-
tive (-5°C). Do not apply both of these
devices in combination with one an-
other.
When compressors are mounted onto
a rack for a multi-evaporator system
(i.e. supermarket) or when evapora-
tors operate at dierent temperatures,
use pressure regulators (Danfoss KVP)
without an MOP expansion valve.

18
SYSTEM DESIGN RECOMMENDATIONS
Operating limits
NTZ – R404A / R507A
Working pressure range, high side (bar gauge) 13.2 – 27.7
Working pressure range, low side (bar gauge) 0.1 – 3.3
Minimum low pressure safety
switch setting (bar gauge) 0
Minimum low pressure pump-down
switch setting (bar gauge) 0.1
Relief valve opening pressure dierence (bar) 30
Relief valve closing pressure dierence (bar) 8
Low ambient temperature
operation At low ambient temperatures, the con-
densing temperature and condensing
pressure in air cooled condensors will
decrease. This low pressure may be
insucient to supply enough liquid
refrigerant to the evaporator. As a re-
sult the evaporating temperature will
decrease, leading to low capacity and
eventual poor oil return. At start-up,
the compressor will pull into vacuum
and it will be switched o by the low
pressure protection. Depending on
how the low pressure switch and delay
timer are set, short cycling can occur.
To avoid these problems, several solu-
tions are possible, based on reducing
condenser capacity:
zLiquid ooding of condensors (note:
this solution requires extra refrig-
erant charge. A non-return valve
in the discharge line is required
and special care should be taken
when designing the discharge line.)
zReduce air ow to condensors
zAlternatively the condensor may be
installed indoor.
When the compressor is located in a
low ambient temperature environ-
ment, increased refrigerant migration
will occur during shut down periods.
For such conditions an extra belt-type
crankcase heater is strongly recom-
mended.
Note that with 100% suction gas
cooled motors, Maneurop® compres-
sors can be externally insulated. Refer
to section "Liquid refrigerant migra-
tion & charge limits" for more details.
Low pressure A low-pressure (LP) safety switch
must also be used; deep vacuum op-
erations will result in failure. The mini-
mum LP safety switch (loss of charge
switch) setting is 0 relative bar (0 bar
g). For systems without pump-down
feature, the LP safety switch must be
either a manual lockout device or an
automatic LP safety switch wired into
an electrical lockout circuit. LP switch
tolerance must not allow for vacuum
operation of the compressor. LP safety
switch settings for pump-down cycles
with automatic reset are listed in the
following table.
High pressure A high-pressure (HP) safety switch is
required to shut down the compressor
should the discharge pressure exceed
the values shown in the table below.
This switch can be set at lower values
depending on the application and
ambient conditions. It must be either
located in a lockout circuit or associ-
ated with a manual reset device to
prevent cycling around the high pres-
sure limit.
If a discharge valve is used, the HP
switch must be connected to the serv-
ice valve gauge port, which cannot be
isolated.

19
SYSTEM DESIGN RECOMMENDATIONS
Motor protection
Discharge temperature
protection
Even when the motor windings are
protected against overheating by the
internal motor protection, the com-
pressor discharge gas temperature
could exceed the maximum allowed
value of 135°C when the compres-
sor is operated outside its application
envelope. The most eective protec-
tion against too high discharge gas
temperature is to mount a discharge
gas thermostat. An accessory kit is
available from Danfoss which includes
Voltage unbalance Operating voltage limits are shown in
the table on page 9. The voltage ap-
plied to motor terminals must lie with-
in these limits during both start-up
and normal operation. The maximum
allowable voltage unbalance is 2%.
Voltage unbalance causes high am-
perage on one or more phases, which
in turn leads to overheating and pos-
sible motor damage.
The voltage unbalance is given by the
following formula:
Cycle rate limit No more than 12 starts per hour (6
when a soft start accessory is used)
are allowed. A higher number would
reduce the service life of the motor-
compressor unit. If necessary, use an
anti-short-cycle timer within the con-
trol circuit.
The system must be designed in a way
that guarantees minimum compressor
running time so as to provide sucient
motor cooling after start-up as well as
proper oil return from the system to
the compressor.
A 5-minute delay between two suc-
cessive compressor starts is being pro-
posed herein, with a 2-minute runtime
after each start and a 3-minute idle
time between each stop and start.
Only during the pump-down cycle
may the compressor run for much
shorter intervals.
Vavg = Mean voltage of phases 1, 2 and 3
V1-2 = Voltage between phases 1 and 2
V1-3 = Voltage between phases 1 and 3
V2-3 = Voltage between phases 2 and 3.
|Vavg - V1-2 |+|Vavg - V1-3 |+|Vavg - V2-3 |
2 xVavg
% voltage unbalance: x 100
Internal motor protection Maneurop® NTZ compressors have a
built-in motor protection which pro-
tects the motor against overheating,
current overload and locked rotor con-
ditions. Additional external overload
protection is not compulsory but may
still be advisable for alarm function
and to avoid the compressor tripping
on its internal protection.
Further an external safety cut-out can
also de-energise the liquid line sole-
noid valve preventing liquid transfer
from the condenser to the evaporator.
Such function can not be handled by
the built-in motor protector.
For the selection of an external motor
protector the RLA (Rated Load Amps)
values from page 9 can be used.
A thermal overload relay shall be se-
lected to trip at not more than 140% of
the RLA value. A circuit breaker shall be
selected to trip at not more than 125%
of the RLA value. Further requirements
for the external protector are:
zOver-current protection; the protec-
tor must trip within 2 minutes at 110%
of the Maximum Continuous Current
(MCC). The MCC value is listed in the
table on page 9 and stamped as A-max
on the compressor nameplate.
zLocked rotor protection; the protec-
tor must trip within 10 seconds on a
start at locked rotor current (LRA)
zSingle phasing protection; the pro-
tector must trip when one of the three
phases fails.

20
SYSTEM DESIGN RECOMMENDATIONS
Liquid refrigerant control
and charge limits
Refrigeration compressors are basi-
cally designed as gas compressors.
Depending on the compressor de-
sign and operating conditions, most
compressors can also handle a limited
amount of liquid refrigerant. Maneu-
rop® NTZ compressors have a large
internal volume and can therefore han-
dle relatively large amounts of liquid
refrigerant without major problems.
However even when a compressor can
handle liquid refrigerant, this will not
be favourable to its service life.
Liquid refrigerant will dilute the oil,
wash out the bearings causing wear
and eventually seizure. Furthermore,
high oil carry over will cause lack of oil
in the sump.
Good system design can limit the
amount of liquid refrigerant in the
compressor, which will have a positive
eect on the compressor service life.
Liquid refrigerant can enter a compres-
sor in various ways, with dierent ef-
fects on the compressor as described
in the following points.
Thermostat
Insulation
Bracket
Discharge line
O-cycle migration During system standstill and after
pressure equalisation, refrigerant will
condensate in the coldest part of the
system which may be the compressor
when it is placed in a cold environ-
ment. Ultimately, the full system re-
frigerant charge can condensate in the
compressor crankcase. A large amount
will dissolve in the compressor oil un-
til the oil is completely saturated with
refrigerant. When the compressor is
started, the pressure in the crankcase
decreases rapidly and refrigerant will
violently evaporate, causing the oil
to foam (boiling). Both dilution and
foaming reduce the lubrication prop-
erties of the oil. In extreme situations
liquid could enter the compressor
cylinders with immediate compressor
break-down as a result.
Liquid oodback during
operation
During normal and stable system
operation, refrigerant will leave the
evaporator in a superheated condition
and enter the compressor as a super-
heated vapour. Normal superheat val-
ues at compressor suction are 5 to 30
K. However the refrigerant leaving the
evaporator can contain an amount of
liquid refrigerant due to dierent rea-
sons:
zwrong dimensioning, wrong setting
or malfunction of expansion device
zevaporator fan failure or frosted-up
evaporator coils.
In these situations, liquid refrigerant
will continuously enter the compres-
sor. The negative eects from continu-
ous liquid oodback are:
zpermanent oil dilution
zin extreme situations with high sys-
tem refrigerant charge and large
amounts of oodback, liquid slug-
ging could occur.
the thermostat, mounting bracket
and insulation. The thermostat must
be attached to the discharge line as
indicated below at no more than
150 mm from the discharge connec-
tion.