15
Scenario C
At an entering water temperature of 55
o
F or less, and with first and second stage cooling being called by the
thermostat (Y1 and Y2), economizer and mechanical cooling will both be active.
Scenario D
At an entering water temperature of 45
o
F or less, and with a call for first stage cooling present from the thermostat
(Y1), economizer will be activated and both compressors will be locked-out. Water temperature is deemed to be
sufficient to provide sufficient cooling capacity without the need for mechanical cooling.
Scenario E
At an entering water temperature of 45
o
F or less, with unit running in economizer mode and a call for second
stage cooling from the thermostat being detected, the unit will turn on compressor 1, until there is no longer a call
for second stage cooling. Economizer will run in tandem with compressor 1 in this scenario.
Scenario F
At an entering water temperature of 45
o
F or less, with unit running in economizer mode and a call for second
stage cooling from the thermostat being detected, the unit will turn on compressor 1. If there is a continuous call
for second stage cooling for more than 20 minutes, compressor 2 will also be activated. Economizer will operate
in tandem with compressors 1 and 2 as long a call for second stage cooling is active from the thermostat (Y2).
Dual Compressor Unit Sequence of Operation
Scenario
Y1
Y2
Entering Water Temp
COMP 1 COMP 2
Water Flow
Economizer
A
ON
OFF
Greater Than 55
o
F
ON
OFF
Condenser Only
OFF
B
ON
OFF
55
o
F Or Less
ON
OFF
Cond and Econo Coil
ON
C
ON
ON
55
o
F Or Less
ON
ON
Cond and Econo Coil
ON
D
ON
OFF
45
o
F Or Less
OFF
OFF
Cond and Econo Coil
ON
E
ON
ON
45
o
F Or Less
ON
OFF
Cond and Econo Coil
ON
F
ON
ON*
45
o
F Or Less
ON
ON
Cond and Econo Coil
ON
* call for Y2 for 20 minutes or more.
Note
:
If the Economizer Activation Set-point is desired to be higher than 55
o
F, the Temperature
“Offset” value of
the
C450CCN-3C
should be adjusted. If the “Offset” value is not increased, lock-out of the compressor will occur
at an EWT higher than that which will allow the economizer coil alone to handle the space cooling load (factory
setting: EAS set point minus 10
o
F).
To adjust
“Offset” value, just go to temperature offset selection screen, press
▲ or ▼ to select the desired temperature offset value, press ► to save. The screen example below shown an
OFFS value of 3 (°F) for Sensor 1. Please refer to
“System 450 Control Module C450CCN-3C Quick Setup
Instruction” for details.
The desired switching set-point for the second relay stage is 45
o
F. Adjustment of the
individual stage differentials is not recommended (excessive valve / compressor cycling may result).
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