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Installer’s Guide
General
Operation of the unit heating and cooling cycles is automatic when
the system is in the HEAT or COOL functions (the optional automatic
changeover thermostat, when in the AUTO position, automatically
changes to heat or cool with an appropriate room temperature
change). The fan can be set to ON, causing continuous evapora-
tor (indoor) fan operation or set to AUTO 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 un-
comfortably humid, it is recommended that the fan only be used in
the AUTO mode.
Cooling Mode
Note that the TSH and TSC are contacts that are internal to the
indoor comfort control.
With the disconnect switch in the ON position, current is supplied
to the compressor 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 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 comfort control set to AUTO 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 de-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 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 comfort control set to ON, 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 units). Starting at the
“R” terminal on the indoor comfort control, current goes through
the system switch (which is in “AUTO” position) to the TSH-1 con-
tacts. 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 compressor
and outdoor fan motor. 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 providing power to the “W” terminal on the
indoor thermostat and to the supplementary heater control circuit.
Note that 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
comfort control. 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.
Sequence of Operation
Starting the Unit in Heating Mode
NOTE: See the section on Sequence of Operation for a descrip-
tion of the heat pump heating operating sequence.
Check that all grills and registers are open and all unit access panels
are closed before start-up.
Set the comfort control above room temperature until achieving a
first stage call for heat and set the fan to AUTO or ON.
Heating Shut Down
Set the comfort control to OFF or at a setting below room temperature.
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 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 out-
door 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) terminates the defrost cycle, or times off after twelve
minutes in defrost, the (DFC) energizes the outdoor fan motor (ODM)
and twelve 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.
Defrost Control
The demand defrost control measures heat pump outdoor
ambient temperature with a sensor located outside the outdoor
coil. A second sensor located on the outdoor coil is used to
measure the coil temperature. The difference between the
ambient and the colder coil temperature is the difference
or delta-T measurement. This delta-T measurement is
representative of the operating state and relative capacity of the
heat pump system. Measuring the change in delta-T determines
the need for defrost. The coil sensor also senses outdoor coil
temperature for termination of the defrost cycle.
NOTE: Refer to the SERVICE FACTS for fault detecting, test sen-
sor, and checkout procedures.
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