OM AGSD-1
15
The electronic expansion valves are operated by the MicroTech II controller to maintain
precise refrigerant control to the evaporator at all conditions.
Standard FanTrol Condenser Fan Control
When the compressor starts, a number of fans may be started, depending on the OAT and
the Forced Fan setpoints. The MicroTech II controller will activate the remaining condenser
fans as needed to maintain proper condenser pressure. The MicroTech II controller
continuously monitors the condenser pressure and will adjust the number of operating
condenser fans as required. The number of condenser fans operating will vary with outdoor
temperature and system load. The condenser fans are matched to the operating compressors
so that when a compressor is off, all fans for that circuit will also be off.
Pumpdown
As the system chilled water load requirements diminish, the compressors will unload. As
the system load continues to drop, the electronic expansion valve will be stepped closed, the
solenoid valve will close, and the refrigerant circuits will go through a pumpdown sequence.
As the evaporator pressure falls below the pumpdown pressure setpoint while pumping
down, the compressor and condenser fans will stop. The unit has a one-time pumpdown
control logic; therefore, if the evaporator pressure rises while the compressor is in the off
state, the controller will not initiate another pumpdown sequence. The circuit controller will
keep the compressor off until the next call for cooling occurs.
The chilled water pump output relay will generally remain energized until the unit is in the
Off State due to the remote stop switch, unit Off switch, BAS command, or keypad setting
calling for the unit to be disabled.
Liquid Line Solenoid Valve (LLSV)
The LLSV cycles with the compressor starter. Its purpose is to provide a positive seal in the
liquid line in the event of a power failure. A power failure may prevent the expansion valve
from closing completely by removing power before the valve steps all the way closed.
Summary of Contents for AGS 225D
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