Danfoss MLZ Evolution A Page 19 Application Manuallines Download

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Electrical data, connections and wiring

The compressor will only operate properly in a
single direction. Use a phase meter to establish
the phase orders and connect line phases L1, L2
and L3 to terminals T1, T2 and T3, respectively.
For three-phase compressors, the motor will run
equally well in both directions. Reverse rotation
results in excessive noise; no pressure differential
between suction and discharge; and suction line
warming rather than immediate cooling.
A service technician should be present at initial
start-up to verify that supply power is properly
phased and that compressor and auxiliaries are
rotating in the correct direction.

MLZ015-048 scroll compressors are designed
to operate for a maximum of 150 hours in
reverse, but as a reverse rotation situation can go
unnoticed for longer periods, phase monitors are
recommended.

For compressors MLZ058 and larger, phase
monitors are required. The selected phase
monitor should lock out the compressor from
operation in reverse.

At brief power interruptions, reverse rotation can
occur with single phase compressors. In this case
the internal protector will stop the compressor.
It will have to cool down and will restart safely
afterwards.

For three-phase applications the voltage
measured at the compressor terminals for each

phase should be within ± 2% of the average for
all phases.

Phase sequence and

reverse rotation

protection

Voltage imbalance

Internal motor protection

MLZ scroll compressors are equipped with an
internal line break protector mounted on the
motor windings. The protector is an automatic
reset device, containing a snap action bimetal
switch.

Internal protectors respond to over-current and
overheating. They are designed to interrupt

motor current under a variety of fault conditions,
such as failure to start, running overload, and fan
failure.

If the internal overload protector trips out, it
must cool down to about 60°C (140°F) to reset.
Depending on ambient temperature, this may
take up to several hours.

Three phase

Suggested wiring diagram
with “one shot” pump down
cycle and safety lock-out relay

Control device .................................................. TH
Optional short cycle timer (3 min) .........180 s
Control relay .................................................... KA
Liquid Line Solenoid valve .........................LLSV
Compressor contactor .................................. KM
Phase monitor ................................................ PM
Safety lock out relay ........................................KS
Pump-down control low pressure switch ..LP
High pressure safety switch........................ HPs
Fused disconnect ............................................Q1
Fuses ...................................................................F1
Compressor motor ...........................................M
Discharge gas thermostat ......................... DGT

DGT

HPs

180 s

CONTROL CIRCUIT