© Danfoss | Climate Solutions | 2022.03
Electrical data, connections and wiring
General wiring
information
The wiring diagrams below are examples for
safe and reliable compressor wiring. In case an
alternative wiring logic is chosen, it is imperative
to respect the following rules:
When a safety switch trips, the compressor must
stop immediately and must not re-start until
the tripping condition is back to normal and
the safety switch is closed again. This applies to
the LP safety switch, the HP safety switch, the
discharge gas thermostat and the motor safety
thermostat.
In specific situations, such as winter start
operation, an eventual LP control for pump-
down cycles may be temporarily bypassed to
allow the system to build pressure. But it remains
mandatory for compressor protection to apply an
LP safety switch. The LP safety switch must never
be bypassed.
Pressure settings for the LP and HP safety switch
and pump-down listed in table from section "Low
pressure".
When ever possible (i.e. PLC control), it is
recommended to limit the possibilities of
compressor auto restart to less than 3 to 5 times
during a period of 12 hours when caused by
motor protection or LP safety switch tripping.
This control must be managed as a manual reset
device.
MLZ/MLM09
Suggested wiring diagrams logic
M
DGT
HP
LPS
180 s
TH
LP
CONTROL CIRCUIT
F1
F1
KM
KM
KM
KA
KA
A1
A2
A3
KA
KA
KS
KS
KS
L1
L3
L2
Q1
T1
T3
T2
LLSV
KS
Wiring diagram with pump-down cycle
KM
L1
L3
L2
Q1
CONTROL CIRCUIT
F1
F1
KM
KA
KA
KS
KS
KS
HP
DGT
TH
180 s
85 52 019 - A
T1
T2
M
T3
KA
KA
A1
A2
A3
Wiring diagram without pump-down cycle
LPS
Fuses ..................................................................................................F1
Compressor contactor ................................................................. KM
Control relay ................................................................................... KA
Safety lock out relay .......................................................................KS
Optional short cycle timer (3 mins) ......................................180 s
External overload protection .......................................................F2
Pump-down pressure switch .......................................................LP
High-pressure safety switch ........................................................HP
Control device .................................................................................TH
Liquid line solenoid valve ........................................................ LLSV
Discharge gas thermostat/thermistor...................................DGT
Fused disconnect ...........................................................................Q1
Motor safety thermostat ............................................................thM
Compressor motor ..........................................................................M
Motor protection module ........................................................MPM
Thermistor chain............................................................................... S
Safety pressure switch .................................................................LPS
Legend
17
AB243586442698en-000601
Application Guidelines
Single compressors