Bryant 542E - Manual (Page 12)

ondary of unit transformer IB.
Energized indoor blower relay coil 2A closes its set of nor­
mally open contacts between 1 and 3, completing the circuit
through indoor blower motor 3D2, and the motor starts.
Energized compressor contactor coil 2D closes its normally
open contacts between 13 and 23, and 11 and 21, completing
the circuit through compressor motor 3F and outdoor fan
motor 3D1. Both motors start instantly. The current flow
through outdoor fan motor 3D1 also flows through fan
switching thermostat 7K which maintains the optimum
cooling mode condensing temperature by switching the fan
motor to high- or low-speed operation, depending on the out­
door ambient temperature.
The heat pump is now operating in the cooling mode. The
energized reversing valve is directing the high-temperature,
high-pressure discharge gas to the outdoor coil where the
heat is transferred to the outdoor air.
All three energized motors will continue to run and the cool­
ing cycle will remain “on” until the room temperature falls
slightly below the room thermostat temperature setting.
When this point is reached, the thermostat cooling bulb will
tilt and break the circuit between thermostat R to terminals
G and Y. These open circuits deenergize indoor blower relay
coil 2A and compressor contactor coil 2D. All closed contacts
return to their normally open position and all three motors
stop.
The heat pump has now returned to a “standby” condition,
awaiting another “call” for cooling by the room thermostat.
If the room temperature should continue to fall, the ther­
mostat cooling operation bulb will tilt and break the circuit
between thermostat terminals R and 0. This open circuit
deenergizes reversing valve solenoid coil 5B and outdoor fan
realy coil 2C. The fan relay contacts open and the reversing
valve switches to the normal heating mode position.
Except for the crankcase heater, all heat pump components
are now deenergized. When the room temperature rises
again and reaches the room thermostat control points, the
cooling sequence will start again. If the room temperature
continues to drop, the heat pump will remain “olT’ and the
heating mode will not start until the room thermostat SYS­
TEM switch is moved to the HEAT position (either HEAT or
AUTO when
using autochangeover thermostat P/N
34427DP115).
C. Heating Operation
With the room thermostat SYSTEM switch in HEAT posi­
tion and the FAN switch in AUTO position, the heating
sequence of operation is as follows:
When the room temperature drops slightly below the ther­
mostat temperature setting, the thermostat first-stage heat­
ing bulb “makes” and thermostat terminal R is connected to
thermostat terminals G and Y. These completed circuits
through the thermostat connect indoor blower relay coil 2A
(through unit terminal G) and compressor contactor coil 2D
(through unit terminal Y) across the 24-volt secondary of
unit transformer IB.
Energized indoor blower relay coil 2A closes its set of nor­
mally open contacts between 1 and 3, completing the circuit
through indoor blower motor 3D2, and the motor starts.
Energized compressor contactor coil 2D closes its normally
open contacts between 13 and 23, and 11 and 21, completing
the circuit through compressor motor 3F and outdoor fan
motor 3D1. Both motors start instantly. Outdoor fan motor
3D1 will operate on high speed regardless of the outdoor
temperature because outdoor fan relay contacts 2C are in
their normal heating mode positions as shown in Figure 16.
In these normal positions, the line-voltage circuit to fan mo­
tor 3D1 is always to the high-speed motor windings, regard­
less of the switching action of fan switching thermostat 7K.
The heat pump is now operating in the heating mode. The
nonenergized reversing valve is in the normal heating mode
position and the high-temperature, high-pressure discharge
gas is being directed to the indoor coil, where the heat is
transferred to the indoor air.
All three energized motors will continue to run and the heat­
ing cycle will remain “on” until the room temperature rises
slightly above the room thermostat temperature setting. If
the outdoor temperature has dropped to the point where the
heating capacity of the heat pump cannot maintain the
desired indoor room temperature, the second-stage heating
bulb will “make” when the indoor temperature continues to
drop to a point slightly below the room thermostat factory
differential setting. Thermostat terminal R is automatically
connected to thermostat terminals W1 and W2. These com­
pleted circuits through the thermostat connect the relay coil
(or coils if using a two- or three-bank heater) of the supple­
mental electric heater across the 24-V secondary of heat
pump transformer IB. The electric heater energizes to pro­
vide supplemental electric heat to the system.
NOTE: See the Installation Instructions packaged with the
electric heater for a more comprehensive description of the
electric heater sequence of operation.
When the room temperature rises slightly above the room
thermostat second-stage heat setting, the second-stage
heating bulb will tilt and break the circuit between ther­
mostat terminal R to terminals W1 and W2. The supplemen­
tal electric heat deenergizes. When the room temperature
continues to rise to a point slightly above the room ther­
mostat temperature setting, the first-stage heating bulb
will tilt and break the circuit between thermostat terminal
R to terminals G and Y. These open circuits deenergize
indoor blower relay coil 2A and compressor contactor coil
2D. All closed contacts return to their normally open posi­
tion and all three motors stop.
The heat pump has now returned to a “standby” condition
awaiting another “call” for heating by the room thermostat.
Except for the crankcase heater, all heat pump components
are now deenergized. If the room temperature continues to
rise, the heat pump will remain “off” and the cooling mode
will not start until the room thermostat SYSTEM switch is
moved to the COOL position (either COOL or AUTO when
using autochangeover thermostat P/N 34427DP115).
D. Defrost Cycle
The defrost control circuit consists of defrost timer 3M,
defrost thermostat switch 7M, and defrost relay 2P. The
defrost timer is factory-set for 90-minute intervals of
elapsed running time, which results in optimum heating
mode efficiency for most installations; however, the adjusta­
ble cam can be reset for a 30-minute interval when abnormal
climatic conditions dictate. The conditions include such
things as excessive outdoor humidity at low outdoor temper­
atures.
CAUTION; The factory-set 90-minute interval should never
be adjusted unless the unit does not completely defrost after
the 10-rainute time-terminated defrost cycle.
With the heat pump operating in the heating mode, the
defrost cycle sequence of operation is as follows:
Defrost thermostat 7M switches to the closed position when
the outdoor coil refrigerant temperature drops to approx­
imately 30°F. When defrost timer 3M completes 90 minutes
of elapsed running time, a coil in the timer energizes and the
normally open timer contacts between 3 and 4 for approx­
imately 10 seconds. (The normally closed timer contacts be­
tween 3 and 5 do not open at this time, as explained later.) If
defrost thermostat switch 7M has not switched close, the
normally open timer contacts return to the open position and
the heat pump continues to operate in the heating mode.
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