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Installer’s Guide
Sequence Of Operation
General
Operation of the unit heating and cooling cycles is automatic for HEAT and COOL
modes. (The optional automatic changeover thermostat, when in the AUTO mode,
automatically changes to heat or cool with sufficient room temperature change.)
The fan ON mode causes continuous evaporator (indoor) fan operation, and the
AUTO mode causes 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 uncom-
fortably 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 thermostat.)
With the disconnect switch in the ON position, current is supplied to the compres-
sor crankcase heater and control transformer. (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 ener gizes the switch-over valve (SOV) and places it in the cooling
posi tion (it is in the heating position when not energized).
When the indoor temperature rises 1-1/2 degrees, TSC-2 contacts close, supplying
power to the “Y” terminal on the indoor thermo stat, and to the compressor contac-
tor (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 sup plied to the com-
pressor 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 thermo-
stat, current goes through the system switch (which is in “AUTO” position) to the
TSH-1 contacts. When closed, these con tacts supply power to terminal “Y” on
the indoor thermostat as well as to the heating anticipator. The switch-over valve
will not ener gize because of the high resistance of the heating anticipator in the
thermostat. Power is provided from “Y” to the compressor contac tor (CC) which
starts the outdoor fan motor and compressor. The indoor thermostat contact TSH-1
also provides power to “G” ter minal 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 provid-
ing power to the “W” terminal on the indoor thermostat and to the supplemen-
tary heater control circuit. NOTE: The fan relay(F) must have been energized.
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 dis able 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 temperature (CBS) and the outdoor ambient tempera-
ture (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 coilOn SCROLL bearing units
only, the control will stop the compressor for a minimum of thirty (30) seconds).
The outdoor coil temperature sensor (CBS) terminates the defrost cycle, or times
off after twelve minutes in defrost, the (DFC) energizes the outdoor fan motor
(ODM) and fifteen seconds later de-ener gizes the (SOV), which returns the unit
to the heating mode. Supple mentary electric heat, if provided, is brought on to
control indoor temperature during the defrost cycle.
ECM Fan Motor Adjustments
(4WHC3042, 048, & 060 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 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 options, and electric heat airflow adjustment. The switches appear as
shown in Figure 6.
Figure 6. ECM Fan Control
CFM
SELECTION
LIGHT
DIP
SWITCHES
