Filter
Top Products
164
CONTROLS (cont)
Continuous Air Circulation — Turn unit power on. Set system
control at OFF position. Set fan switch at ON position. The
indoor-fan contactor is energized through the thermostat switch
and the indoor fan runs continuously.
Cycle-LOC™ Protection — If unit operation is interrupted by
an open high-pressure switch, low-pressure switch, indoor coil
freezestat, or by compressor internal line-break device (over-
current or overtemperature), and compressor is calling for
either cooling or heating, Cycle-LOC protection device simulta-
neously locks out unit and lights a warning light on the thermo-
stat. 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 overcurrent
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 freez-
estat, 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 (thermostat 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 — 542J150,180
Cooling, Units Without Economizer — With unit main power
on, set thermostat to COOL position and desired room tempera-
ture. 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 motors start. If
the 5-minute compressor time-delay (CTD) on the defrost board
(DB) is satisfied, then compressor no. 1 (542J180) or unloaded
compressor (542J150) 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 542J180 units, with an additional rise in room temperature,
cooling contactor no. 2 in the thermostat closes, energizing
compressor contactor no. 2. Compressor no. 2 starts and
cycles on demand of the thermostat to satisfy the occupied
space demands.
On 542J150 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 and compressor(s)
energize. The economizer damper moves to vent position.
Upon a first-stage call for cooling, when outdoor ambient tem-
perature is below the temperature control setting, the indoor fan
starts and economizer damper modulates to maintain mixed-air
temperature. The compressor(s) remains off.
Upon a second-stage call for cooling, compressor no. 1
(542J180) or loaded compressor (542J150) is energized and
mechanical cooling is integrated with economizer cooling. Com-
pressor no. 2 (542J180) 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 compres-
sor can be reenergized.
Heating, Units Without Economizer — With unit main power
on, set thermostat at HEAT position and desired room tempera-
ture. 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), reversing valve
relay (RVR), reversing valve solenoids (RVS1 and RVS2) and
compressor no. 2 contactor. Compressor (size 150) or com-
pressor no. 2 (size 180) and indoor and outdoor fan motors
start. If the 5-minute CTD on the DB is satisfied, then compres-
sor 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, ener-
gizing 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) posi-
tion.
On a drop in room temperature, heating contactor no. 1 in the
thermostat closes, energizing heat relay (HR), reversing valve
relay (RVR), reversing valve solenoids (RVS1 and RVS2) and
compressor no. 2 contactor. Compressor no. 2 (size 180) and
indoor and outdoor fan motors start. If the 5-minute CTD on the
DB is satisfied, then compressor (542J150) or compressor no. 1
(180) contactor is energized and compressor (542J150) or
compressor no. 1 (180) will start. The outdoor-air damper stays
at vent position while the indoor fan is operating.
On units equipped with electric heat, when additional heat is
needed, heating contactor no. 2 in the thermostat closes, ener-
gizing 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 defrost 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 energizes the electric heat. The
outdoor-fan motor will stop.
The unit continues to defrost either until the coil temperature as
measured by DFT1 or DFT2 reaches 65 F, or until unit com-
pletes a 10-minute defrost cycle.
During the defrost mode, when a circuit defrosts, RVS will oscil-
late 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 applica-
ble) will be deenergized, the reversing valve solenoids will be
energized, and the outdoor fans will start.