Cooling Mode; Starting The Unit In Heating Mode; Heating Shutdown; Demand Defrost Operation - Trane 2/4WCC30 Series Installer's Manual

IMPORTANT: De-energize the main power disconnect ONLY
when servicing the unit. Power may be required to keep the heat
pump compressor warm and to boil off refrigerant in the compres-
sor.

Starting the Unit in Heating Mode

Note: See the section on "Sequence of Operation" for a
description 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.
Slowly set the thermostat above room temperature until achieving
a first stage call for heat and place the fan switch in the AUTO or ON
position.
Heating Shut Down
Place the system selector switch at OFF or place the heating
selector lever at a setting below room temperature.
Sequence of Operation
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 switch can be placed in the ON position, causing
continuous evaporator (indoor) fan operation or placed in the
AUTO position causing fan operation to coincide with heating or
cooling run cycles.

Cooling Mode

Note that the TSH and TSC are contacts that are internal to the
indoor thermostat.
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 system switch in the AUTO position and TSC-1 contacts
closed, power is supplied to the "O" terminal on the indoor thermo-
stat 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 de-energized).
When the indoor temperature rises 1-1/2 degrees, TSC-2 contacts
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 transformer. (The
outdoor fan relay (ODF) is energized through normally closed
contacts on the defrost timer control (DFC) on the 460V units).
Installer's Guide
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 resis-
tance of the heating anticipator in the thermostat. Power is provided
from "Y" to the compressor contactor (CC) which starts the
compressor and outdoor fan motor. 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" 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
thermostat. When placed in the emergency heat position, it will
disable the compressor, bypass the outdoor thermostats, if pro-
vided, 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 temperature (ODS-B) and calcu-
lates 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) 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-energizes the (SOV),
which returns the unit to the heating mode. Supplementary 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
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 sensor,
and checkout procedures.
delta-T measurement is
Page 21