Operation Sequence − Compressor; Single-Phase Compressor Startup; Three Phase Compressor Startup - Lennox HP21 Unit Information

B−Operation Sequence − Compressor

Single-Phase Compressor Startup

Figure 26 shows single-phase compressor windings. This
compressor has a two speed capacitor-start, capacitor-run
motor. For starting, the start and run capacitors are in par-
allel to provide the proper starting torque.
capacitor is disconnected by the start relay when the com-
pressor comes up to speed. The run capacitor remains
connected to the start winding and the motor runs as a two-
phase induction motor with improved power factor and
torque characteristics provided by the capacitor.
Low speed compressor operation is provided by powering
the run windings (internally connected in series) from ter-
minals 1 (common) and 7. The windings form a four-pole
motor operating at 1800 RPM. The four low speed start
windings are in series and are connected to terminals 1
(common) and 8. They are used with the start and run ca-
pacitors and start relay to start and bring the motor up to
speed.
High speed compressor operation is provided when the run
windings are connected in parallel; terminals 1 (common)
and 7 to L1 and terminal 2 to L2. The windings form a two-
pole motor operating at 3600 RPM. The two high speed
start windings are in series and connected to terminals 1
(common) and 3.

Three Phase Compressor Startup

Figure 27 shows the windings of three-phase two-speed
compressors. The compressors have two-speed, three-
phase induction motors. Capacitors are not needed to
provide the proper phase and torque characteristics.
Low speed operation is provided when the motor windings
are connected in a series Delta" circuit. The motor oper-
ates at 1800 RPM.
High speed operation is provided when the motor windings
are connected in a parallel Delta" circuit. Normally closed
contacts on the low speed contactor provide this connec-
tion.
SINGLE-PHASE MOTOR WINDINGS LOW SPEED
The start
START
CAP.
SINGLE-PHASE MOTOR WINDINGS HIGH SPEED
START
CAP.
THREE-PHASE MOTOR WINDINGS LOW SPEED
THREE-PHASE MOTOR WINDINGS HIGH SPEED
Page 29
MOTOR LEAD TERMINALS
1
COMMON
2
7
RUN WINDINGS
RUN
CAP.
HIGH SPEED
START WINDINGS
3
8
LOW SPEED
START WINDINGS
START RELAY
MOTOR LEAD TERMINALS
1
COMMON
2
7
RUN WINDINGS
RUN
CAP.
HIGH SPEED
START WINDINGS
3
8
LOW SPEED
START WINDINGS
START RELAY
FIGURE 26
SERIES DELTA" CIRCUIT
L1 T1
T6
L2
T2
T5
L3
PARALLEL DELTA" CIRCUIT
L1 T4
COMPRESSOR
CONTACTOR K1−1
T1
L2
T6 T2
L3
FIGURE 27
T4
T3
T3
T5