Carrier 542E - Manual (Page 13)

B. Cooling Operation
With the room thermostat SYSTEM switch in the COOL
position and the FAN switch in the AUTO position, the cool­
ing sequence of operation is as follows:
When the room temperature rises to within 2 degrees of the
cooling control setting of room thermostat, the thermostat
cooling operation bulb tilts and connects thermostat ter­
minal R to thermostat terminal O. This completed circuit
through the thermostat completes the circuit through unit
terminal O. Reversing valve solenoid coil 5B and outdoor fan
relay coil 2C are now connected across the 24-volt secondary
of unit transformer IB.
Energized solenoid coil 5B switches the reversing valve from
the normal heating mode position to the cooling mode posi­
tion. Energized outdoor fan relay coil 2C closes its set of nor­
mally open contacts between 1 and 3, and opens its set of
normally closed contacts between 1 and 2, permitting two-
speed outdoor fan motor 3D1 to operate on either high or low
speed, depending on the outdoor ambient temperature.
NOTE: When the contacts of outdoor fan relay 2C are in
their normal heating mode positions as shown in Figure 13,
fan motor 3D1 operates on high speed, regardless of the out­
door ambient temperature.
The heat pump is now in the “standby” condition and ready
to operate in the cooling mode when the room thermostat
“calls” for cooling.
When the room temperature rises to a point that is slightly
above the cooling control setting of the thermostat, the ther­
mostat cooling bulb tilts and thermostat terminal R is auto­
matically connected to thermostat terminals G and Y. These
completed circuits through the thermostat connect indoor
blower relay coil 2A (through unit terminal G) and com­
pressor contactor coil 2D (through unit terminal Y) across
the 24-volt secondary of transformer IB.
The set of normally open contacts of energized relay 2A be­
tween 1 and 3 closes and completes the circuit through
indoor hlower motor 3D2. The motor starts instantly.
The two sets of normally open contacts of energized contac­
tor 2D between 13 and 23, and 11 and 21, close and complete
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 continue to run and the cooling
cycle remains “on” until the room temperature drops to a
point that is slightly below the cooling control setting of the
room thermostat. At this point, the thermostat cooling bulb
tilts and breaks the circuit between thermostat R to ter­
minals 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 hy the room thermostat.
If the room temperature continues to fall, the thermostat
cooling operation bulb will tilt and break the circuit be­
tween thermostat terminals R and 0. This open circuit
deenergizes reversing valve solenoid coil 5B and outdoor fan
relay 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 “ofT’, and the
heating mode will not start until the room thermostat
SYSTEM 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 the HEAT
position and the FAN switch in the AUTO position, the heat­
ing sequence of operation is as follows:
When the room temperature drops to a point that is slightly
below the heating control setting of the thermostat, the
thermostat first-stage heating bulb “tilts” and thermostat
terminal R is automatically connected to thermostat ter­
minals G and Y. These completed circuits through the ther­
mostat 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 transformer IB.
The set of normally open contacts of energized relay 2A be­
tween 1 and 3 closes and completes the circuit through
indoor hlower motor 3D2. The motor starts instantly.
The two sets of normally open contacts of energized contac­
tor 2D between 13 and 23, and 11 and 21, close and complete
the circuit through compressor motor 3F and outdoor fan
motor 3D1. Both motors start instantly. Outdoor fan motor
3D1 operates on high speed, regardless of the outdoor tem­
perature, because outdoor fan relay contacts 2C are in their
normal heating mode positions, as shown in Figure 13. In
these normal positions, the line-voltage circuit to fan motor
3D1 is always to the high-speed motor windings, regardless
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 continue to run, and the heating
cycle remains “on” until the room temperature rises to a
point that is slightly above the heating control setting of the
room thermostat. If the outdoor temperature has dropped to
the point where the heating capacity of the heat pump can
not maintain the desired indoor room temperature, the
second-stage heating bulb will tilt when the indoor tem­
perature continues to drop to a point that is slightly below
the factory differential setting of the room thermostat.
Thermostat terminal R is automatically connected to ther­
mostat terminals W1 and W2. These completed circuits
through the thermostat connect the relay coil (or coils if
using a two- or three-bank heater) of the supplemental
electric heater across the 24-V secondary of heat pump
transformer IB. The electric heater energizes to provide sup­
plemental 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 to a point that is slightly
above the second-stage control 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 that is slightly above the heating
control setting of the room thermostat, the first-stage heat­
ing bulh tilts and breaks the citcuits between thermostat
terminal R to terminals G and Y. These open circuits
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