Lennox HP21 Installation and operation manual

Page 1 ©1994 Lennox Industries Inc.
Corp. 9434−L12
HP21
Service Literature
EARLY/LATE MODEL
Revised 07−2007
HP21 SERIES UNITS INCLUDING TSC−2, TSC−3 AND TSC-6
The HP21 is a high efficiency residential split-system heat
pump with a two-speed compressor. Early models include
HP21−411, −511 and −651. Late models built after March 1,
2000 include HP21−36, −48 and −60. All models are avail-
able in sizes ranging from 3 through 5 tons in either single
or three-phase configuration. Early and late models feature
solid-state two-speed control and new solid-state demand
defrost control. The two-speed control regulates compres-
sor speed in response to thermostat demand during
cooling mode. Compressor speed is regulated by outdoor
air temperature during heating mode. The defrost control
monitors outdoor air temperature and liquid line tempera-
ture to determine when defrost is needed. The series uses
conventional heat pump circuitry with expansion valves in
the outdoor and indoor units.
This manual is divided into sections which discuss the com-
ponents, refrigerant system, charging procedures,
maintenance and operation sequences. All specifications
in this manual are subject to change.
DANGER
Electric Shock Hazard.
May cause injury or death.
Line voltage is present at all compo-
nents when unit is not in operation on
units with single pole contactors.
Disconnect all remote electrical power
supplies before opening unit panel.
Unit may have multiple power supplies.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person-
al injury or loss of life. Installation and service must
be performed by a qualified installer or service
agency.
WARNING
Refrigerant can be harmful if it is inhaled. Refrigerant
must be used and recovered responsibly.
Failure to follow this warning may result in person-
al injury or death.
TABLE OF CONTENTS
General 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifications / Electrical 2. . . . . . . . . . . . . . . . . . . . . .
I Application 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II Unit Components 3. . . . . . . . . . . . . . . . . . . . . . . . . . .
TSC−2 Control 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TSC−3 Control 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
TSC−6 Control 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III Refrigerant System 20. . . . . . . . . . . . . . . . . . . . . . . . .
IV Charging 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V Maintenance 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VI Miscellaneous 26. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII Wiring Diagrams and Operating Sequence 27. . . .

Page 2
ELECTRICAL DATA
SPECIFICATIONS
Model No. HP21−411
HP21−413
HP21−511
HP21−513
HP21−651
HP21−653
Outdoor Coil
Outdoor Fan
Refrigerant−22 (charge furnished)
Face area (sq.ft.)
Tube diameter (in.)
No. of Rows
Fins per inch
Diameter (in.)
No. of Blades
Motor hp
Cfm
Rpm
Watts
Liquid line connection (sweat)
Vapor line connection (sweat)
Model No.
Line voltage data − 60hz.
Compressor
Rated load amps
Power factor
Locked rotor amps
Outdoor Coil
Fan Motor
Full load amps
Locked rotor amps
Max fuse or circuit breaker size (amps)
*Minimum circuit ampacity
HP21−511
HP21−48−230
HP21−513
HP21−48−233
HP21−651
HP21−60−230
HP21−653
HP21−60−233
208/230/1ph 208/230/3ph208/230/3ph 208/230/1ph208/230/1ph 208/230/3ph
334
90.0 60.0 90.0 60.0 141.0 91.0
outside / inside
18.22/
17.53
21.64/
20.81
23.92/
23.01
3/8 3/8 3/8
222
18 18 20
24 24 24
1/10 1/6 1/4
3120 3200 4200
820 815 815
200 310155
13lbs. 10oz. 15lbs. 5oz. 18lbs. 10oz.
3/8 3/8 3/8
3/4 7/8 1−1/8
17.6 12.7 17.6 12.7 30.8 19.9
.98 .90 .98 .90 .92 .90
0.7 0.7 1.0 1.0 1.7 1.7
1.2 1.2 1.9 1.9 2.9 2.9
40 25 40 25 60 45
22.7 16.6 23.0 16.9 40.2 27.0
HP21−411
HP21−36−230
HP21−413
HP21−36−233
HP21−36−230
HP21−36−233
HP21−48−230
HP21−48−233
HP21−60−230
HP21−60−233
*Refer to National Electrical Code Manual to determine wire, fuse and disconnect size requirements.
NOTE − Extremes of operating range are plus 10% and minus 5% of line voltage

Page 3
FIGURE 1
HP21 ELECTRICAL COMPONENTS
COMPRESSOR B1
HIGH PRESSURE
SWITCH S4
REVERSING VALVE
AND SOLENOID L1
COMPRESSOR
TERMINAL BOX
SERVICE LIGHT
THERMOSTAT S54
CRANKCASE
THERMOSTAT S40
UNIT CONTROL
AMBIENT AIR PORT
(DEFROST CONTROL
AMBIENT SENSOR)
DEFROST CONTROL
LIQUID LINE SENSOR
I−APPLICATION
All major components (indoor blower/coils) must be
matched according to Lennox recommendations for the
compressor to be covered under warranty. Refer to Engi-
neering Handbook for approved system matchups. A
misapplied system will cause erratic operation and can re-
sult in early failure of compressor or other components.
II−UNIT COMPONENTS
A−Control Transformer T19
All units are equipped with a line voltage to 24VAC trans-
former which supplies power to unit controls as shown in
table 1. Refer to unit wiring diagram for detailed information
regarding unit wiring.
B−Contactors K1 and K69
The compressor is energized by a set of contactors located
in the control box. Contactors in HP21 units are energized
as shown in table 2.
TABLE 1
HP21 Component Source of Power
24VAC from
Outdoor Unit
Transformer T19
Contactor K1
Contactor K69
Crankcase Thermostat S40
High Pressure Limit S4
24VAC from
Indoor Unit
Transformer T1
Two-Speed Control A14
Defrost Control CMC1
Defrost Relay K4
Speed Control Thermostat S55
Service Light Thermostat S54
Line Voltage
Potential Relay K31
Crankcase Heater HR1
Compressor Run Capacitor C5
Compressor Start Capacitor C7
Bleed Resistor R21
Fan Capacitor C1
Ambient Thermistor RT3
Compressor B1
Outdoor Fan B4

Page 4
FIGURE 2
HP21 CONTROL BOX COMPONENTS
CONTACTOR K1
DEFROST CONTROL
CMC1
START CAPACITOR C7
(single-phase only)
DUAL CAPACITOR C12
(single−phase)
EARLY HP21 -1 / -2 / -3 SINGLE PHASE SERIES UNITS USE FAN
CAPACITOR C1 AND COMPRESSOR CAPACITOR C5 IN PLACE OF
C12
24V TERMINAL
STRIP TB15
START RELAY K31
(single-phase only)
DEFROST RELAY
K4
CONTACTOR K69
TWO-SPEED CONTROL
A14
SPEED CONTROL
THERMOSTAT S55
TRANSFORMER
T19
OUTDOOR FAN CAPACITOR C1
(three-phase only)
Contactor K1
Contactor K1 energizes low speed compressor operation
in all units (single-phase and three-phase.) In single−phase
units K1 is a two pole contactor with two sets of normally
open contacts and in three−phase units K1 is a five pole
contactor with three sets of normally open contacts and two
sets of normally closed contacts. K1 is also equipped with a
set of single-pole double-throw auxiliary contacts located
on the side of the contactor. The contactor is energized in
response to low speed thermostat demand (from two-
speed control jackplug J44/P44 pin 9.)
TABLE 2
Compressor Speed Single-Phase Three-Phase
Low
High
K1 K1
K1 & K69 K69
Contactors Energized
In single-phase units, K1 also de-energizes the crankcase
heater during compressor operation.
Contactor K69
Contactor K69 energizes high speed operation in all units
(single-phase and three-phase.) In single−phase units K69
is a five−pole contactor with three sets of normally open
contacts and two sets of normally closed contacts. In three−
phase units K69 is a three−pole contactor with three sets of
normally open contacts.This contact arrangement pro-
vides unique switching characteristics for two-speed
operation. K69 is also equipped with a set of single-pole
double-throw auxiliary contacts located on the side of the
contactor. The contactor is energized in response to high
speed thermostat demand from JP44-8 (two-speed control
jackplug J44/P44 pin 8.)
Contactor Operation: Single-Phase Units
Low speed demand energizes K1. K1 de-energizes the
crankcase heater and energizes the compressor. High
speed demand energizes both contactors K1 and K69. K69
N.O. contacts close to redirect the circuit to the high speed
start windings and the N.C. contacts open to de-energize
the low speed start windings. K69 N.C. contacts also switch
whenever K69 is energized to ensure that K1 is energized
with K69 during high speed operation (refer to unit wiring
diagram).
Contactor Operation: Three-Phase Units
Low speed demand energizes K1. K1 energizes the com-
pressor and locks out contactor K69. High speed demand
de−energizes K1 and energizes contactor K69. K69 locks
out K1 and energizes the compressor on high speed.
K1 is wired so that when de−energized, the contactor forms
a parallel common connection to the motor windings for
high speed forming a parallel Delta" connection for Cope-
land compressors. When K1 is energized, the contactor
forms a series Delta connection to the compressor wind-
ings. Refer to operation sequence in back of this manual for
more information.
C−Defrost Relay K4
All HP21 units are equipped with a defrost relay located
in the unit control box which controls defrost. The relay is
a 3PDT relay powered 24 VAC from the thermostat. K4 is
enabled during both cooling and heating modes (except
emergency heat). It is only powered when the defrost
control is calling for defrost. When energized, the revers-
ing valve and indoor auxiliary heat are energized.
Simultaneously, the outdoor fan is de-energized. K4
latches in for the duration of the defrost period.

Page 5
D−Hard Start Relay K31 (single-phase only)
All single-phase HP21 units are equipped with a hard start
relay located in the unit control box which controls the op-
eration of the compressor starting circuit. The relay is normally
closed when the compressor (contactor K1) is de-energized.
Capacitor (C7) is connected in series to a set of normally
closed K31 contacts and assists the compressor in starting.
When K1 energizes, the compressor immediately begins start-
up. K31 remains de-energized during compressor start-up and
the start capacitor (C7) remains in the circuit. As the compres-
sor gains speed K31 is energized by electromotive forces
generated by the compressor. When K31 energizes, its con-
tacts open to take the start capacitor out of the circuit.
E−Terminal Strip TB15
All HP21 units are equipped with a low voltage terminal
strip located in the unit control box for making up thermo-
stat wiring connections (refer to figure 2).
F−Compressor B1
See ELECTRICAL DATA or compressor nameplate for
specifications. Figure 3 shows the compressor terminal
box. All compressors are equipped with internal pressure
relief valves set at 450+50 psig. Compressors in all units
use insertion type crankcase heaters which are regulated
by relays in the HP21.
FIGURE 3
T3 T8 T1 T7
SINGLE
PHASE
T2
S1 S2
TYPICAL TWO-SPEED COMPRESSOR
TERMINAL BOX
COPELAND SINGLE-PHASE SHOWN
G−Outdoor Fan Motor B4
The specifications table on page 1 of this manual shows the
specifications of outdoor fans used in all HP21 units. In
single-phase units, the outdoor fan is controlled by the
compressor contactor and is de−energized when the de-
frost relay is energized. In three-phase units, the outdoor
fan is controlled by contactor K10 and is de-energized
when the defrost relay is energized. See figure 4 if outdoor
fan motor replacment is necessary.
FAN GUARD
Condenser fan
and motor Wiring
Drip loop
FIGURE 4
1/4"
H−High Pressure Limit S4
All units are equipped with a high pressure limit mounted on
the compressor discharge line. The switch can be manual-
ly reset and has a cutout" point of 410+10 psig. The switch
is electrically connected in series with crankcase thermo-
stat S40 in the two-speed control’s safety circuit. When
tripped, the TSC interrupts unit operation. If the high pres-
sure switch trips" three times within the same thermostat
demand, the two-speed control locks out and the contactor
cannot energize.
Although the high pressure limit must be reset manually, if
the two-speed control is locked out it must be reset before
the unit can operate. To reset the control, break and re-
make thermostat demand.
I−Crankcase Thermostat S40
Crankcase thermostat S40 is electrically connected in se-
ries with high pressure limit S4 in the two-speed control’s
safety circuit. It is used in all units to monitor the tempera-
ture of the compressor. The switch is a N.C. SPST
belly-band" thermostat strapped to the compressor.
The switch is factory preset to trip at 190°F+5°F on a tem-
perature rise. When tripped, the TSC interrupts unit
operation. The crankcase thermostat automatically resets
when the compressor crankcase drops below 110°F+7°F. If
the crankcase thermostat trips" three times within the
same thermostat demand, the two-speed control locks out
and the contactor cannot energize. If the two-speed control
is locked out it must be reset before the unit can operate. To
reset the control, break and remake thermostat demand.

Page 6
J−Service Light Thermostat S54
All units are equipped with a service light thermostat mounted
on the compressor discharge line. The switch is electrically
connected to the service light in the indoor thermostat. When
compressor discharge line temperature reaches 130+5°F,
the switch opens. If discharge line temperature drops below
110+5°F during unit operation (indicating a problem in the
system), the switch closes. If thermostat demand is present
when S54 closes, the service light is powered to indicate ser-
vice is needed.
K−Start Capacitor C7
All single-phase HP21 units are equipped with a start ca-
pacitor connected in parallel with the run capacitor. The
capacitor is switched off by the potential relay when the
compressor nears full speed. The start capacitor is rated
145−175mfd. @ 330VAC in all single-phase units.
Three-phase HP21 units do not use start capacitors.
L−Bleed Resistor R21
All single-phase HP21 units are equipped with a bleed re-
sistor connected in parallel with start capacitor C7. The
resistor is used to slowly discharge the capacitor when not
in use. R21 is a 15,000 ohm 2 watt resistor.
M−Run Capacitor C5
All single-phase early model HP21 -1 / -2 / -3 units use a
compressor run capacitor to maximize motor efficiency.
The run capacitor is located in the unit control box and is
electrically connected as shown in the unit wiring diagram.
Run capacitors are wired in parallel with the start capacitor.
See side of capacitor for ratings.
N−Fan Capacitor C1
All early model HP21 -1 / -2 / -3 single phase and all HP21
three−phase series units (regardless of dash number) use
single-phase PSC outdoor fan motors which require an ex-
ternal run capacitor. The fan capacitor is located inside the
unit control box. See side of fan capacitor for ratings.
O−Dual Capacitor C12
HP21-4 / -5 and late model single-phase units use a single
dual capacitor to maximize motor efficiency in both the fan
motor and the compressor, which use PSC motors. A dual
capacitor has two independent capacitors inside one can.
Each side of the capacitor has different ratings . See side of
capacitor for ratings. The dual capacitor is wired in parallel
with the start capacitor and is electrically connected as shown
in the unit wiring diagram.
P− Two-Speed Controls
ELECTROSTATIC DISCHARGE (ESD)
Precautions and Procedures
CAUTION
Electrostatic discharge can affect electronic
components. Take precautions during unit
installation and service to protect the unit’s
electronic controls. Precautions will help to
avoid control exposure to electrostatic dis-
charge by putting the unit, the control and the
technician at the same electrostatic potential.
Neutralize electrostatic charge by touching
hand and all tools on an unpainted unit surface
before performing any service procedure.
TSC−2 Two-Speed Control
The TSC two-speed control (figure 5) is a Lennox built con-
trol designed for use with two-speed condensing units and
heat pumps. The control provides automatic switching
from low speed to high speed operation and back. The
TSC−2 is designed for use with Bristol and Copeland com-
pressors. All HP21 series units use Copeland
compressors. All early model HP21−1 units use the TSC−2
controls.
The TSC two-speed control contains relays which energize
compressor operation in response to thermostat demand.
High speed operation can be energized and de−energized
without passing through low speed. The control also con-
tains safety timed−off delays and compressor
over−temperature sensing which help protect the compres-
sor.

Page 7
TSC-2 TWO-SPEED CONTROL
FIGURE 5
123
456
789
JP44
JP44−1 24VAC POWER (INPUT)
JP44−2 24VAC NEUTRAL (GROUND)
JP44−3 NOT USED
JP44−4 2nd STAGE THERMOSTAT DEMAND
JP44−5 THERMOSTAT COMMON (C)
JP44−6 1st STAGE THERMOSTAT DEMAND
JP44−7 24VAC FROM SAFETY SWITCHES
TO INTERNAL CONTACTOR COIL (INPUT)
JP44−8 HIGH SPEED (24VAC OUTPUT)
JP44−9 LOW SPEED (24VAC INPUT)
S1 and S2
TO COMPRESSOR WINDING
TEMPERATURE SENSORS
TOP VIEW
JP44
RED DIAGNOSTIC LED
S1 MANUAL OVERRIDE
OF 5 MINUTE DELAY
A timed−off delay in the control prevents the compressor
from operating for five minutes after the end of a thermostat
demand or after a power failure to prevent short cycling
(see miscellaneous section.) The control also counts unit
fault conditions." Whenever the compressor stops due to a
safety limit trip or if the compressor winding temperature
becomes too hot, the control’s internal cycle counter accu-
mulates one fault. If three unit faults are counted during the
same thermostat demand, the control locks out" and stops
all unit operation. The control can be reset by breaking and
remaking thermostat demand. Also, unit faults are erased
when power is interrupted. When thermostat demand
changes stages, compressor operation stops for approxi-
mately one minute to allow refrigerant pressure to equalize
in the system.
In order to aid servicing and troubleshooting, a manual
override button has been placed on the control. The manu-
al override button, when pressed and released, bypasses
the five minute delay so low speed or high speed operation
can be immediately energized.
A red LED located on the face of the control can be used for
diagnostics. The control continually self-tests its internal
circuits and uses the diagnostic LED to indicate control fail-
ure or Safety Dormant Lockout. A Safety Dormant Lockout
is caused by abnormal line voltage (such as a lightning
strike near the unit).
Normal Operation Sequence
1− General Operation
On power−up, the control begins a ten second initial
power−up delay.
2− The control then begins a five minute delay during
which the unit is not operational (control and outdoor
unit do not respond to thermostat demand.) Once the
five minute delay is complete, the control waits in
OFF mode for thermostat demand.
3− After receiving a thermostat demand, the TSC delays
three seconds before responding.
4− Low speed demand (JP44−6) energizes low speed op-
eration (JP44−9) OR high speed demand (JP44−4)
energizes high speed operation (JP44−8.)
5− During unit operation, if low speed demand changes to
high speed demand or if high speed demand changes
to low speed, the control delays three seconds before
responding. Then, all unit operation stops for 60+5
seconds (control de−energizes JP44−8 and JP44−9.)
This allows refrigerant pressure to equalize in the sys-
tem. At the end of the 60+5 second delay, the control
responds to whatever thermostat demand is present. If
no thermostat demand is present, the control resets
(see unit fault conditions section) and the control re-
turns to step 2 above.
6− If thermostat demand stops compressor operation, all
unit operation stops after a three second delay (control
de−energizes JP44−8 and JP44−9,) the control resets
(see unit fault conditions section) and the control re-
turns to step two.

Page 8
Two-Speed Control Fault Conditions
If the control is in low speed operation, high speed opera-
tion, OFF" mode or speed change delay, the control
counts" or accumulates faults on an internal cycle counter.
Only faults which occur during compressor operation and
which cause the compressor to shut off are counted. After a
fault is counted, the control stops unit operation, resets and
begins a five minute time delay (step 2, operation se-
quence). If the control senses a fault at the end of five
minutes, the unit will not restart. If the control counts three
faults during the same thermostat demand, the control
locks out unit operation.
NOTE−If the control locks out, it can be reset by break-
ing thermostat demand for about five seconds then
remaking thermostat demand. Also, anytime thermo-
stat demand is removed or power is interrupted, the
control resets to zero faults.
A fault occurs when
1− Compressor operation is monitored by high pressure
switch and crankcase temperature thermostat. These
controls are wired in series. If either one trips, com-
pressor operation is interrupted and one fault is
counted. High pressure switch must be reset manually
but crankcase temperature switch resets automatical-
ly.
IMPORTANT-If the cycle counter counts three faults
during the same thermostat demand, the control locks
out. The outdoor unit remains inoperable until thermo-
stat demand is broken. This indicates further
troubleshooting is needed. Though the control can be
reset by breaking thermostat demand, the unit may re-
main inoperable. The high pressure or high
temperature conditions may still exist and must be lo-
cated and corrected before the unit can be placed back
in service.
It is likely that the control could count three unit faults
from the crankcase temperature switch during a single
thermostat demand since this switch resets automati-
cally. However, the cycle counter can only count unit
faults from the high pressure switch if the reset button
is pushed without interrupting thermostat demand.
2− On all units using the TSC two-speed control, terminals
S1 and S2 on the control are connected to temperature
sensors (thermistors) which monitor the temperature
of the compressor motor windings. The two-speed
control measures the resistance through the sensors.
The sensors increase their resistance as temperature
increases (for example, too much superheat). When
the resistance through the sensors increases above a
preset limit, the control stops compressor operation.
As the compressor windings cool, the resistance
through the sensors drops below the reset limit, the
control resets automatically and one fault is counted.
NOTE-Intermittent continuity (bad connection or failing
components) can cause false lockout or lit LED. Check
all electrical connections thoroughly.
The sensors can be checked by measuring resistance
(ohms) through the sensors with the wires discon-
nected from the control (unit not running). The sensor
wires are not polarity sensitive. Table 3 shows winding
temperature sensor resistance values which will cause
the TSC to lock out. When the unit is operating normal-
ly, the resistance through the sensors should be below
the trip value shown in table 3.
The control can be checked by comparing the resist-
ance measured through the sensors to the voltage
measured across the sensor terminals with the unit
running. Table 4 shows voltage measured across two-
speed control terminals S1 and S2 with the
compressor running.

Page 9
TABLE 3
Compressor Winding
Temperature Sensor
Trip Ohms
Temp. Rise
Reset Ohms
Temp. Fall
TSC−2 Bristol or Copeland
Compressor 25K to 35K 8.4K to 10K
Two-Speed Control Manual Override
The manual override button is designed to be an aid in ser-
vicing and troubleshooting the control or the unit. When the
button is pushed and then released, the control bypasses
the five minute override delay.
Reset
Range
TABLE 4
Resistance Through
Compressor Winding
Temperature Sensor
K-ohms (ohms x 1000)
Voltage Across TSC Ter-
minals S1 and S2 with
Unit Running
DC Volts +.15
0
1.0
5.5
6.9
8.4
10.0
16.0
20.0
24.0
25.0
30.0
35.0
.02
.92
3.4
3.9
4.3
4.7
5.6
6.0
7.0
6.8
6.3
---
Trip
Range
+−
DC volts
Measured with unit running.
COMPRESSOR WINDING SENSOR
OPERATING RANGE
Do not use the override button for eleven seconds after
power-up. If the button is pushed during the ten second
power-up delay, the button has no effect. The control com-
pletes the five minute delay.
LED OFF"
MAY MEAN UNIT FAULT" CONDITION
If the unit will not run and the LED is not lit, a unit lockout
condition is indicated. Breaking and remaking thermostat
demand will reset the control. Activate the compressor by
pressing and releasing the override button (see illustra-
tion). If compressor starts, the control is good and should
not be replaced. Proceed through the troubleshooting flow-
chart in the Unit Information Manual to locate the source of
the lockout. If the compressor does not start, a problem
probably exists elsewhere in the unit. Check the unit volt-
age and proceed through the unit troubleshooting
flowchart in the Unit Information Manual.
LED ON"
MEANS TSC FAULT" CONDITION
If the unit will not run and the LED is lit, the TSC may be in
Safety Dormant Lockout (a lockout caused by self-test fail-
ure or high voltage spike).
To determine if the control is in Safety Dormant Lockout,
briefly turn off power at the disconnect. When power is re-
stored, check the LED. If the LED is lit, the control is
damaged and must be replaced. If the LED is not lit, the
control is probably good and should not be replaced until
eliminated by all other checks. Confirm this by activating
the compressor (press and release the override button with
thermostat demand present). If the compressor starts, the
control was in safety dormant lockout (due to high voltage
spike or self-test failure) and the control should not be re-
placed. If the compressor does not start, the control is
probably good and the problem is located elsewhere in the
unit. Proceed through the troubleshooting flowchart to lo-
cate the problem. Start by checking all manually reset
controls (high pressure switch etc...)
Service Instructions:
1− If light comes on and stays lit, turn off power at dis-
connect for at least 3 seconds.
NOTE−Breaking thermostat demand will not reset the
control if the control is in a Safety Dormant Lockout.
2− If LED is on when power is restored, replace TSC.
3− If light goes out see troubleshooting flowchart in
Unit Information Manual.

Page 10
TSC-3 Two-Speed Control
All early model HP21 -2 series units (single and three
phase) are equipped with a TSC-3 two-speed control. The
speed-control thermostat (formerly key number S55) has
been removed from the unit and incorporated into the cir-
cuitry of the TSC-3 control (see figure 6). The function and
operating sequence are otherwise identical to the TSC-2
plus the separate thermostat used in previous HP21 units.
The purpose of the speed control thermostat is to force the
compressor to operate on high speed when outdoor tem-
perature is low. It initiates a speed change delay and
automatically energizes high speed when temperature
drops below the setpoint. The setpoint is factory preset and
can be field adjusted.
FIGURE 6
TSC-3 TWO-SPEED CONTROL
(with built in speed control thermostat)
J44
SCREWDRIVER
TSC
TWO-SPEED CONTROL
SENSOR
TEMPERATURE
ADJUSTMENT
(potentiometer)
When temperature rises above the setpoint, the control
initiates a speed change delay and automatically ener-
gizes low speed.
The setpoint can be changed by adjusting the poten-
tiometer shown in figure 6. The potentiometer is factory
set as shown in table 5.
TABLE 5
Speed Control Thermostat
Adjustable Range
Cut-In
(Close on Temperature Drop)
Min. Factory
Setting Max
.
Cut-Out
(Open on Temperature Rise)
37+2°F 42+2°F 55+2°F
47+2°F 52+2°F 65+2°F
Mid.
46+2°F
56+2°F
To adjust the speed control thermostat, insert a small
slot screwdriver into the potentiometer as shown in fig-
ures 6 and 7. To lower the setpoint, turn the
potentiometer counter-clockwise. To raise the setpoint,
turn the potentiometer clockwise. Do not force the po-
tentiometer to turn past its stops; the potentiometer will
be damaged.
FIGURE 7
TSC-3 TWO-SPEED CONTROL
WINDING TEMPERATURE
SENSOR TERMINALS
TEMPERATURE
SENSOR TEMPERATURE ADJUSTMENT
(shown in factory position)
OVERRIDE
BUTTON
(5 minute delay)
The unit wiring diagrams have been revised to reflect the
changes for the HP21-2 (TSC-3), and are shown in section
VII−Wiring Diagrams and Operation Sequence.