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Sequence of Operation
GENERAL
Operation of the unit heating and cooling cycles is automatic for
HEAT
and
COOL
functions. (The optional automatic changeover
thermostat, when in the
AUTO
position, automatically changes
to heat or cool with sufficient room temperature change.) The fan
switch can be placed in either the
ON
position, causing continu-
ous evaporator (indoor) fan operation, or the
AUTO
position
causing fan operation to coincide with heating or cooling run
cycles. Continuous fan mode during cooling operation may not be
appropriate in humid climates. If the indoor air exceeds 60%
relative humidity or simply feels uncomfortably humid, it is
recommended that the fan only be used in the AUTO mode.
COOLING MODE
(NOTE:
TSH
&
TSC
are contacts internal to the indoor thermo-
stat.)
With the disconnect switch in the
ON
position, current is sup-
plied to the compressor crankcase heater and control trans-
former. (The outdoor fan relay
(ODF)
relay is energized through
normally closed contacts on the defrost timer control
(DFC)
on
the 460V and 600V units only.) The cooling cycle is enabled
through the low voltage side of the control transformer to the
“R”
terminal on the indoor thermostat. With the system switch in the
AUTO
position and
TSC-1
contacts closed, power is supplied to
the
“O”
terminal on the indoor thermostat to the switchover
valve coil
(SOV)
. This energizes the switch-over valve
(SOV)
and places it in the cooling position (it is in the heating position
when not energized).
When the indoor temperature rises 1-1/2 degrees,
TSC-2
con-
tacts close, supplying power to the
“Y”
terminal on the indoor
thermostat, and to the compressor contactor
(CC)
. This starts
the outdoor fan motor and compressor. The
TSC-2
contacts also
provide power to the
“G”
terminal which provides power to the
fan relay
(F)
starting the indoor fan motor.
HEATING MODE
With the disconnect switch in the
“ON”
position, current is
supplied to the compressor crankcase heater and control trans-
former. (The outdoor fan relay
(ODF)
is energized through
normally closed contacts on the defrost timer control
(DFC)
on
the 460V and 600V units.) Starting at the
“R”
terminal on the
indoor thermostat, current goes through the system switch
(which is in
“AUTO”
position) to the
TSH-1
contacts. When
closed, these contacts supply power to terminal
“Y”
on the indoor
thermostat as well as to the heating anticipator. The switch-over
valve will not energize because of the high resistance of the
heating anticipator in the thermostat. Power is provided from
“Y”
to the compressor contactor
(CC)
which starts the outdoor
fan motor and compressor. The indoor thermostat contact
TSH-
1
also provides power to
“G”
terminal on the indoor thermostat
energizing the fan relay
(F)
, which starts the indoor fan motor
SUPPLEMENTARY HEAT
The supplementary electric heat
is brought on when the
indoor temperature drops 1-1/2 degrees below the thermostat
setting.
TSH-2
contacts close providing power to the
“W”
termi-
nal on the indoor thermostat and to the supplementary heater
control circuit.
NOTE:
The fan
relay
(F)
must have been ener-
gized. An outdoor thermostat may have been added to disallow
the second stage (if provided) of electric heat above a selected
outdoor temperature. If the outdoor temperature falls below the
setting on the outdoor thermostat, this additional heater stage
will come on. When the outdoor air temperature rises, and the
outdoor T-stat setpoint is reached, the system will revert back to
first stage electric heating.
When the indoor ambient is satisfied,
TSH-2
contacts will open
and the unit will revert back to the compressor only heating
mode and then off. For
emergency heat
(use of supplementary
electric heat only), an emergency
(EMERG)
heat switch is
provided within the thermostat. When placed in the emergency
heat position, it will disable the compressor, bypass the outdoor
thermostats, if provided, and engage the supplementary electric
heaters and indoor fan.
DEMAND DEFROST OPERATION
During the heating cycle, the outdoor coil may require a defrost
cycle which is determined by the demand defrost control
(DFC)
.
This control continuously measures the outdoor coil tempera-
ture
(CBS)
and the outdoor ambient temperature
(ODS-B)
and
calculates the difference or delta-T measurement. When the
calculated delta-T is met, the demand defrost control
(DFC)
opens the circuit to the outdoor fan motor
(ODM)
and energizes
the switch-over valve
(SOV)
, placing the unit in the cooling mode
to defrost the outdoor coil
On SCROLL bearing units only, the
control will stop the compressor for a minimum of thirty (30)
seconds)
. The outdoor coil temperature sensor
(CBS)
termi-
nates the defrost cycle, or times off after twelve minutes in
defrost, the
(DFC)
energizes the outdoor fan motor
(ODM)
and
fifteen seconds later de-energizes the
(SOV)
, which returns the
unit to the heating mode. Supplementary electric heat, if pro-
vided, is brought on to control indoor temperature during the
defrost cycle.
ICM FAN MOTOR ADJUSTMENTS (WCH048, 060F ONLY)
If the airflow needs to be increased or decreased, see the Airflow
Table in the Service Facts. Information on changing the speed of
the blower motor is in the Blower Performance Table.
Blower speed changes are made on the ICM Fan Control mounted
in the control box. The ICM Fan Control controls the variable
speed motor.
There is a bank of 8 dip switches (See Figure 5), located at the
upper left side of the board. The dip switches work in pairs to
match the cooling/heat airflow (CFM/TON), Fan off-delay op-
tions, and electric heat airflow adjustment. The switches appear
as shown in Figure 5.
5
ICM FAN CONTROL
CFM
SELECTION
LIGHT
DIP
SWITCHES
