Service Light Thermostat; Start Capacitor; Run Capacitor; Tsc−2 Two-Speed Control - Lennox HP21 Unit Information

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
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
over−temperature sensing which help protect the compres-
sor.
Page 6
series units use Copeland
delays and compressor