Operating Sequence - Bryant 542F Manual

BASE UNIT OPERATING SEQUENCE
Cooling, Units Without Economizer — With unit main power
on, set thermostat at 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 contact no. 1 in the ther-
mostat closes, energizing compressor no. 1 contactor on all
units. Compressor no. 1, indoor-fan motors, and outdoor-fan
motors start. Compressor no. 1 cycles on demand of thermostat
to satisfy room conditions.
With an additional rise in room temperature, cooling contact
no. 2 in the thermostat closes, energizing compressor contactor
no. 2. Compressor no. 2 starts. Compressor no. 2 cycles on de-
mand of the thermostat to satisfy room conditions.
Heating, Units Without Economizer — Turn power on and set
thermostat at HEAT position and desired temperature. Set fan
at AUTO. (on demand) or ON (continuous) position.
On a drop in room temperature, heating contact no. 1 in the
thermostat closes, energizing compressor contactor no. 1 and
reversing valve, and starting compressor no. 1. Indoor blower
contactors and outdoor-fan contactors energize at the same
time for heat pump cycle.
When thermostat second-stage heating contacts close, com-
pressor contactor no. 2 energizes and compressor no. 2 starts.
Units have a built-in electric resistance heat lockout through the
defrost thermostat. Above 40 F (approximate) outdoor tempera-
ture, electric resistance heat is locked out and second-stage
heat is from compressor no. 2. Below 40 F (approximate) am-
bient temperature, when the thermostat first-stage heating con-
tacts close, compressor contacts no. 1 and no. 2 energize
sequentially through a time delay. Both compressors (no. 1 and
no. 2) are brought on to satisfy heating requirements.
On a further drop in room temperature (outdoor ambient below
40 F), the thermostat second-stage heating contacts close, en-
ergizing the electric resistance heat contactor and starting
second-stage heat. Electric heaters with 2 or more contactors
can have outdoor thermostats wired into the control circuit for
additional staging.
Automatic Changeover — When the system selection switch
is set at AUTO. position, unit automatically changes from heat
operation to cooling operation when the temperature of the con-
ditioned space rises to cooling lever setting. When the tempera-
ture of the conditioned space falls to heating lever 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 position. The
indoor-fan contactor is energized through the thermostat switch
and the indoor fan runs continuously.
Defrost Cycle — The defrost thermostat on the outdoor coil ac-
tivates a defrost timer which energizes electric resistance heat-
ers and deenergizes reversing valve relays and outdoor-fan
motors. When the defrost thermostat is satisfied or when
10 minutes have elapsed, reversing valve solenoids energize
and electric heaters deenergize. The defrost timer will energize
the electric heaters every 90 minutes, if necessary.
The defrost thermostat, in conjunction with a time-delay relay,
prevents electric heat operation above an ambient temperature
of approximately 40 F (depending on coil frost conditions). If de-
frost thermostat closes, time-delay relay energizes, closing
compressor contactor no. 2. Both compressors now operate
from W1, and W2 controls electric heat.

OPERATING SEQUENCE

Cooling, Units With Economizer
Outdoor Air Enthalpy Above Set Point — Indoor and outdoor
fans and compressors energize when there is a call for cooling.
The economizer damper moves to VENT position.
Outdoor Air Enthalpy Below Set Point — Indoor fan starts and
economizer damper opens fully on a first-stage call for cooling.
Compressor remains off.
Compressor is energized and mechanical cooling integrates
with economizer cooling upon a second stage call for cooling.
Economizer damper modulates when mixed-air temperature is
below mixed-air thermostat setting.
A freeze protection thermostat is located on the indoor coil. It
detects ice build-up and turns off the compressor, thus allowing
the coil to clear. Once ice melts, the compressor can be
reenergized.
Heating, Units With Economizer — Outdoor-air damper stays
at VENT position while indoor-air fan runs.
NOTE: If fan switch is at ON position, and room thermostat is
satisfied, damper goes to ventilation position.
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 simultaneously locks out unit and
lights a warning light on the thermostat. Restart the unit by
manually turning room thermostat to OFF and then 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 room thermostat.
ACCESSORY OPERATING SEQUENCES
Emergency Heat — If compressor is inoperative due to a
tripped safety device (high-pressure, low-pressure, indoor-coil
freezestat, overcurrent, or overtemperature), Cycle-LOC™
locks out compressor and lights a warning light on the room
thermostat. When switch is on (thermostat is moved to the EM
HT position), compressor circuit and outdoor thermostats are
bypassed, and second stage of thermostat energizes indoor
blower and electric resistance heaters.
Time Guard Control Circuit — The accessory Time Guard
control circuit provides a 5-minute delay of compressor restart
after desired space temperature has been attained and room
thermostat has shut down the compressor. Assuming that com-
pressor has been off for at least 5 minutes due to room thermo-
stat action, Time Guard control circuit sequence is as follows:
With fan selector switch at AUTO. position and a call for cooling
from the room thermostat, indoor blowers start immediately;
outdoor-air fans and compressor start 15 seconds later. When
room thermostat is satisfied, compressor shuts off. The Time
Guard control circuit timer motor then runs for 4 minutes and
45 seconds, at which point its internal switches reset so normal
sequence can begin again.
The base unit contains, as standard equipment, a factory-
installed Cycle-LOC compressor protection device. If overload
protector causes the compressor to shut off, compressor
remains locked out until control circuit is manually reset. Reset
manually by moving system selector lever on room thermostat
to OFF position momentarily and then returning it to cooling po-
sition. After a standard 5-minute Time Guard control circuit de-
lay, the compressor can restart.
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