Trane Heat Pump Manual: cnt03600 Manual and TSC Trane Operations

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 continuous evaporator (indoor) fan operation, or the AUTO position causing fan operation to coincide with heating or cooling run cycles.

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 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 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 de-energized).

When the indoor temperature rises 1-1/2 degrees, TSC-2contacts 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-2contacts 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 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-1contacts. 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 compressor and outdoor fan motor. The indoor thermostat contact TSH-1also 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-2contacts close providing power to the “W” terminal on the indoor thermostat and to the supplementary 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-2contacts 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. 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.

ICM FAN MOTOR ADJUSTMENTS

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 15), located at the upper right side of the board. The dip switches work in pairs to match the cooling/heat pump airflow (CFM/TON), Fan off-delay options, and electric heat airflow adjustment. The switches appear as shown in Figure 15.

t	ICM FAN CONTROL
	CFM	DIP
	SELECTION	DIP
	LIGHT	SWITCHES
	DIP SWITCHES (TYPICAL SETTINGS)

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