Controls | (10, 15 Ton) |
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SEQUENCE OF UNIT OPERATION
Refer to the unit wiring schematic pasted to the inside of the control panel cover when reviewing the control sequence described below.
Refer to the legend on the previous page for an explanation of the abbreviations used in this sequence.
10-Ton Operation
With fused disconnect switch closed, power is supplied to the crankcase heaters and the
Starting the chilled water pump closes the CWPS auxiliary contacts and completes the flow switch.
When the water temperature rises above theWTT’s set point, its first stage switch closes, allowing power to pass through CWPS auxiliary contacts, the flow switch, the LTC, the ASCT1, the RR1 contacts, the LPC01, and the HPC01 to energize the CC1 coil.This starts compressor number one and the outdoor fan.
If compressor number one can’t satisfy the cooling demand,WTT’s 2nd stage switch closes, allowing power to pass through the CC1 auxiliary contacts, the DBC, the ASCT2, the RR2 contacts, the LPC02, and the HPC02 to energize the CC2 coil which starts compressor number two.
15-Ton Operation
With fused disconnect switch closed, power is supplied to the crankcase heaters, and the
Starting the chilled water pump closes the CWPS auxiliary contacts and completes the flow switch, allowing power to pass through the LTC to energize the CWFIR.
When the water temperature rises above theWTT’s set point, its first stage switch closes, allowing power to pass through the CWFIR contacts, the ASCT1, the RR1 contacts, the LPC01, and the HPC01 to energize the CC1 coil.This starts compressor number one and outdoor fan number one.
If compressor number one can’t satisfy the cooling demand,WTT’s second stage switch closes, allowing power to pass through the CWFIR contacts, the DBC, the ASCT2, the RR2 contacts, the LPC02, and the HPC02 to energize the CC2 coil. This starts compressor number two and outdoor fan number two.
LOW AMBIENT OPERATION
Field Installed Head Pressure Control Accessory
Standard units will operate in outdoor ambient temperatures down to the values shown in the “General Data” section of this catalog. This accessory will enable units to operate down to much lower temperature extremes (see “General Data” section of this catalog).
Head pressure control for CGA units is regulated by means of a
When discharge pressure is 270 psig or higher, the condenser fan runs at full speed. At pressures between 270 psig and 180 psig, the fan speed is adjusted (increased or decreased) in direct relation to the pressure, with minimum fan speed (10 percent of rated motor rpm) occurring when the pressure reaches 180 psig. At pressures below 180 psig, the fan will not run.When discharge pressure rises to 180 psig, the fan will start and run at the reduced speed. Fan speed will continue to increase, as the pressure increases, until full speed is reached at 270 psig.
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