Carrier WEATHERMASTER 50HJQ004-016 Product Data page 166

Controls (cont)
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.
Sequence of operation — 50HJQ014,016
Cooling, units without economizer — With unit main
power on, set thermostat to COOL position and desired
room temperature. Set fan switch at AUTO. (on demand)
or ON (continuous) position.
On a rise in room temperature, cooling contactor no. 1
in the thermostat closes. The indoor and outdoor fan mo-
tors start. If the 5-minute compressor time-delay (CTD) on
the defrost board (DB) is satisfied, then compressor no. 1
(50HJQ016) or unloaded
contactor is energized and compressor will start.
Compressor cycles on demand of the thermostat to satisfy
room conditions. Each time the cooling contactor no. 1
opens, the CTD starts the 5-minute delay.
On 50HJQ016 units, with an additional rise in room
temperature, cooling contactor no. 2 in the thermostat clos-
es, energizing compressor contactor no. 2. Compressor
no. 2 starts and cycles on demand of the thermostat to sat-
isfy the occupied space demands.
On 50HJQ014 units, compressor runs fully loaded on a
call for second-stage cooling.
Cooling, units with economizer — Upon a call for
cooling, when outdoor ambient temperature is above the
temperature control setting, the indoor and outdoor fans
166
compressor (50HJQ014)
and compressor(s) energize. The economizer damper
moves to vent position.
Upon a first-stage call for cooling, when outdoor ambi-
ent temperature is below the temperature control setting,
the indoor fan starts and economizer damper modulates to
maintain mixed-air temperature. The compressor(s) re-
mains off.
Upon a second-stage call for cooling, compressor no. 1
(50HJQ016) or loaded compressor (50HJQ014) is ener-
gized and mechanical cooling is integrated with economiz-
er cooling. Compressor no. 2 (50HJQ016) is locked out. If
the air temperature is below 50 F, a cooling lockout switch
prevents the compressor(s) from running.
When supply-air temperature drops below a fixed set
point, the economizer damper modulates to maintain the
temperature at the fixed set point.
A freeze protection thermostat (FPT) is located on the
indoor coil. It detects frost build-up and turns off the
compressor(s), allowing the coil to clear. Once frost has
melted, the compressor can be reenergized.
Heating, units without economizer — With unit main
power on, set thermostat at HEAT position and desired
room temperature. Set fan switch at AUTO. (on demand)
or ON (continuous) position.
On a drop in room temperature, heating contactor no. 1
in the thermostat closes, energizing heat relay (HR), revers-
ing valve relay (RVR), reversing valve solenoids (RVS1 and
RVS2) and compressor no. 2 contactor. Compressor (size
014) or compressor no. 2 (size 016) and indoor and out-
door fan motors start. If the 5-minute CTD on the DB is
satisfied, then compressor no. 1 contactor is energized and
compressor no. 1 will start.
On units equipped with electric heat, when additional
heat is needed, heating contactor no. 2 in the thermostat
closes, energizing W2.
Heating, units with economizer — With unit main
power on, set thermostat at HEAT position and desired
room temperature. Set fan switch at AUTO. (on demand)
or ON (continuous) position.
On a drop in room temperature, heating contactor no. 1
in the thermostat closes, energizing heat relay (HR), revers-
ing valve relay (RVR), reversing valve solenoids (RVS1 and
RVS2) and compressor no. 2 contactor. Compressor no. 2
(016) and indoor and outdoor fan motors (014,016) start.
If the 5-minute CTD on the DB is satisfied, then compres-
sor (014) or compressor no. 1 (016) contactor is energized
and compressor (014) or compressor no. 1 (016) will start.
The outdoor-air damper stays at vent position while the in-
door fan is operating.
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