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Power is required to keep the heat pump compressor warm and boil off refrigerant in the compressor. STARTING THE UNIT IN THE HEATING MODE NOTE: See the section on "Sequence of Operation" for a description of the heat pump heating operating sequence. Check to make sure all grilles an registers are open an all unit access doors are closed before start-up. Slowly set the thermostat above rom 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. Page 14 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 TSC1 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-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 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 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: 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 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 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. The outdoor coil temperature sensor (CBS) terminates the defrost cycle,...

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