OPERATING SEQUENCES
569D072-120, 576C120 — At start-up, the thermostat calls for cooling. With all safety devices satisfied, the compressor contactor and fan contactor energize, causing the compressor and outdoor-fan motor to operate. Thermostat contacts energize, allowing the field-supplied and field-installed indoor- fan contactor to function. A field-supplied and field-installed liq- uid line valve also opens, allowing the system to function in Cooling mode. As cooling demand is satisfied, the thermostat contacts break, deenergizing the contactor and causing the system to shut off. The liquid line solenoid valve closes, mini- mizing the potential for refrigerant migration. The compressor does not restart until the thermostat again calls for cooling. The system is protected with a safety circuit so that the system will not start if a fault exists (i.e., high or low pressure fault). To reset the safety circuit, set the thermostat to eliminate the cooling demand, then return to original set point. This should be done only once, and if system shuts down due to the same fault, determine the problem before attempting to restart the system.
566D150-240 — When the first stage of cooling thermostat closes, the timer starts. After approximately 3 seconds, the timer activates the compressor and fan motor no. 1 contactors. When the liquid pressure builds to approximately 257 psig, fan motor no. 2 is energized.
When there is demand for additional cooling capacity, the second stage of the cooling thermostat closes, energizing a field-supplied liquid line solenoid (LLS) valve, which opens. This increases the suction pressure, causing the compressor to operate at higher capacity (compressor loads).
When the fan switch is set at AUTO, the indoor-air fan cycles with the compressor. When the switch is set at CONT, the indoor-air fan runs continuously.
At shutdown, the Time Guard II timer prevents the compressor from restarting for approximately 5 minutes.
In addition, an LLS valve wired in parallel with the compressor contactor coil shuts off the liquid line to prevent refrigerant migration back to the compressor during the off cycle.
569F120 — When the thermostat calls for stage one cooling at start-up, and all safety devices are satisfied, the compressor contactor no. 1 (C1) energizes causing compressor no. 1 and outdoor-fan motor no. 1 to start (the indoor-fan contactor should be wired to start at the same time as the compressor). The liquid line solenoid (LLS) valve will open when compressor no. 1 starts, allowing refrigerant to flow in the system.
When the thermostat calls for stage two cooling, compressor contactor no. 2 (C2) energizes causing compressor no. 2 and outdoor-fan motor no. 2 to start. As the cooling demand decreases, stage two on the thermostat opens, causing compressor no. 2 and outdoor-fan motor no. 2 to shut down. As
the cooling continues to decrease, stage one of the thermostat opens causing compressor no. 1 and outdoor-fan motor no. 1 to shut down. The LLS valve for each compressor will close when the associated compressor stops, minimizing the potential for refrigerant migration during the off cycle.
The indoor-fan motor will stop if the thermostat is set to AUTO and will continue to operate if the thermostat is set to CONT. Each compressor is protected with a Cycle-LOCTMdevice so that the compressor will not operate if there is a high-pressure fault, low pressure fault, or a compressor is off due to internal line break overcurrent/overtemperature protection. To reset the Cycle-LOC device, set the thermostat higher to remove the cooling demand, then return to the original set point. This should be done only once. If the system shuts down with the same fault, the cause for the fault should be determined and corrected before the a Cycle-LOC device is reset again.
566E150-240 — At start-up, when the thermostat calls for first stage cooling and all safety devices are satisfied, the compres- sor contactor (C1) energizes causing compressor no. 1 and fan motor no. 1 to start. Fan motor no. 2 will start when the fan cycling pressure switch (FCPS) closes as discharge pressure builds (refer to physical data table for FCPS specifications). With the indoor-fan contactor wired to TB2-4 and TB2-9 contacts on the terminal block, the indoor fan will also start with the compressor. The liquid line solenoid (LLS) valve will open when compressor no. 1 starts, allowing refrigerant to flow in the system.
When the thermostat calls for stage two cooling, compressor contactor no. 2 (C2) energizes causing compressor no. 2 to start. As the cooling demand decreases, stage two on the thermostat opens, causing compressor no. 2 to shut down. As the cooling continues to decrease, stage one of the thermostat opens causing compressor no. 1 and outdoor-fan motor to shut down. The LLS valve for each compressor will close when the associated compressor stops, minimizing the potential for refrigerant migration during the off cycle.
The indoor-fan motor will stop if the thermostat is set to AUTO and will continue to operate if the thermostat is set on CONT. Each compressor is controlled by the thermostat so they will not start until there is a demand from the thermostat. Each compressor is protected with a Cycle-LOC device so that the compressor will not operate if there is a high-pressure fault, low-pressure fault, or compressor is off due to internal line break overcurrent/overtemperature protection. To reset the a Cycle-LOC device, set the thermostat higher to remove the cooling demand, then return to the original set point. This should be done only once. If the system shuts down with the same fault, the cause for the fault should be determined and corrected before the a Cycle-LOC device is reset again.
