Product data

28
On units equipped with electric heat, when additional
heat is needed, heating contactor no. 2 in the thermostat
closes, energizing W2.
Defrost cycle — When the temperature of the outdoor
coil drops below 28 F as sensed by the defrost thermostat
(DFT1 or DFT2), the defrost timer starts. At the end of a
timed period (field set at 30, 50, or 90 minutes), the de-
frost cycle will begin. The defrost board energizes terminals
O and W2, energizes the defrost relay (DR), deenergizes
the reversing valve solenoids (RVS1 and RVS2), and ener-
gizes the electric heat. The outdoor-fan motor will stop.
The unit continues to defrost either until the coil tempera-
ture as measured by DFT1 or DFT2 reaches 65 F, or until
unit completes a 10-minute defrost cycle.
During the defrost mode, when a circuit defrosts, RVS will
oscillate between heating and cooling modes until defrost
mode is complete. This will prevent the head pressure
from getting too high.
At the end of the defrost cycle, the electric heaters (if appli-
cable) will be deenergized, the reversing valve solenoids will
be energized, and the outdoor fans will start.
Automatic changeover — When the system selection
switch is set at AUTO. position, unit automatically changes
from heating operation to cooling operation when the
temperature of the conditioned space rises to the cooling
level setting. When the temperature of the conditioned
space falls to the heating level setting, unit automatically
changes from cooling to heating operation (with a 3 F
deadband in between).
Continuous air circulation — Turn unit power on. Set
system control at OFF position. Set fan switch at ON posi-
tion. The indoor-fan contactor is energized through the
thermostat switch and the indoor fan runs continuously.
Cycle-LOC™ protection — If unit operation is interrupt-
ed by an open high-pressure switch, low-pressure switch,
indoor coil freezestat, or by compressor internal line-break
device (overcurrent or overtemperature), and compressor
is calling for either cooling or heating, Cycle-LOC protec-
tion device simultaneously locks out unit and lights a warn-
ing light on the thermostat. Restart the unit by manually
turning thermostat to OFF and then to ON position. If any
of the protective devices opens again, the unit continues to
lock out until corrective action is taken.
NOTE: If the unit fails to operate due to compressor over-
current condition, restart by manually resetting circuit
breakers at the unit. Restart cannot be accomplished at the
room thermostat.
Emergency heat — If compressor is inoperative due to a
tripped safety device (high or low pressure, indoor coil
freezestat, overcurrent, or overtemperature), the Cycle-
LOC device locks out the compressor and lights a warning
light on the room thermostat. When the switch is on (ther-
mostat is set to the EM HT position), compressor circuit
and outdoor thermostats are bypassed, and the second
stage of thermostat energizes the indoor blower and the
electric resistance heaters.
Application data
Outdoor installation — Units approved for outdoor in-
stallation only.
Ductwork — Secure vertical discharge ductwork to roof
curb. For horizontal discharge applications, either attach
ductwork to unit, or use field-supplied flanges attached to
the horizontal discharge openings and attach all ductwork
to flanges.
Horizontal discharge conversion — To convert from
vertical discharge to horizontal discharge (Durablade econ-
omizer only):
1. Remove economizer or two-position damper to gain
access to return duct opening.
2. Move the horizontal-discharge duct opening covers to
the vertical discharge openings.
3. Rotate economizer or two-position damper 90 degrees.
4. Rotate the barometric relief damper 90 degrees.
5. Install block-off plate over the opening on the access
panel.
Horizontal EconoMi$er — A field-installed accessory
for horizontal discharge applications. Field-installed power
exhaust accessory also available for vertical or horizontal
EconoMi$er applications.
Thru-the-bottom power connections — For applica-
tions requiring thru-the-bottom connections, Carrier acces-
sory thru-the-bottom package must be purchased to ensure
proper connections.
Thermostat — Use of 2-stage heating and cooling ther-
mostat is recommended for all units. A 2-stage cooling
thermostat is required on units with accessory economizer
to provide integrated cooling. A two-stage thermostat is re-
quired for all 50HJQ008-016 units.
Heating-to-cooling changeover — All units are auto-
matic changeover from heating to cooling when automatic
changeover thermostat and subbase are used.
Airflow — Units are draw-thru on cooling and blow-thru
on heating.
Maximum airflow — To minimize the possibility of con-
densate blow-off from indoor coil, airflow through units
should not exceed 500 cfm/ton.
Controls (cont)