A
PPLICATION
GUIDELINES
E
LECTRICAL
DATA
,
CONNECTIONS
AND
WIRING
MLZ / MLM single phase scroll compressors are
designed to operate without any assistance. If
starting within the defined voltage range, PSC
wiring is sufficient.
PSC wiring with a run capacitor only is the default
wiring solution for single phase MLZ and MLM
compressors.
The start winding (C-S) of the motor remains in
circuit through a permanent (run) capacitor. This
permanent (run) capacitor is connected between
the start winding (S) and the run winding (R).
If the starting torque of the PSC wiring is not suf-
ficient due to pressures not fully equalized during
the off-cycle or some voltage drop during start-
ing, the PTCSCR wiring might be an option. PTC-
SRC wiring provides more motor torque than PSC
wiring but less than CSR wiring. The PTC is wired in
parallel to the run capacitor.
When starting the compressor, the PTC, which is at
low resistance, provides additional starting current
to the motor’s start winding. The current passing
through the PTC causes it to heat up and, at a cer-
tain temperature, change to a very high resistance.
At this time the motor is up to nominal speed and
the run capacitor determines the current through
the start winding. The PTC remains at high tem-
perature and thus at high resistance as long as
power is connected to the compressor. When the
compressor is switched off, the PTC cools down to
its initial low resistance and becomes available to
support the next compressor start.
It is important to provide sufficient time between
motor starts to allow the PTC to cool down close
to ambient temperature. Depending on the am-
bient conditions and the cooling of the PTC, this
may take about 5 minutes. A restart before the
PTC is back to low resistance may be successful
or the motor may stall in a locked-rotor state de-
pending on the ambient and system’s conditions.
A locked-rotor state causes the internal protector
to open and would cause even further delay until
the overload is reset.
The following PTC types are recommended for the
MLZ/MLM single phase compressors:
Electrical connections
PSC wiring
PTCSCR wiring
Winding resistance
Winding resistance is the resistance between in-
dicated terminal pins at 77°F (resistance value
± 7%).
Winding resistance is generally low and it requires
adapted tools for precise measurement. Use a dig-
ital ohm-meter, a ‘4 wires’ method and measure
under stabilised ambient temperature. Winding
resistance varies strongly with winding tempera-
ture ; If the compressor is stabilised at a different
value than 77°F, the measured resistance must be
corrected with following formula:
a + t
amb
R
tamb
= R
77°F
a + t
77°F
t
77°F
: reference temperature = 77°F
t
amb
: temperature during measurement (°F)
R
77°F
: winding resistance at 77°F
R
amb
: winding resistance at t
amb
coefficient a= 390
Model
Voltage code 1
208-230 V/1~/60 Hz
Voltage code 5
220-240 V/1~/50 Hz
MLZ/MLM015
305C12*
305C9* / 305C11*
MLZ/MLM019
305C9* / 305C11*
305C9* / 305C11*
MLZ/MLM021
305C9* / 305C11*
305C9* / 305C11*
MLZ/MLM026
305C12*
305C9* / 305C11*
MLZ/MLM030
305C9* / 305C11*
305C9* / 305C11*
MLZ/MLM038
305C9* / 305C11*
305C9* / 305C11*
Note: MLZ compressors with PTCSCR are not approved by UL. It is the customers’ responsibility to get final approval for the system
when required.
16
FRCC.PC.016.A1.22
N
L₁
Run capacitor
PTC
Thermostat
C
S
R
IOL
N
L₁
Run capacitor
Thermostat
C
S
R
IOL
