Trane CVGF500 Installation, Operation & Maintenance Manual page 111

High Lift Unloading Valve and copper lines do not exist. The LLID (1A9) with the High
Lift Unloading relay always exists.
Note: There is noticeable noise, due to gas flow, when the high lift unloading valve is
open.
Functional Description
The following equation determines action of the high lift unloading function:
Trigger IGV% = 0.98 * Lift + ¬
0.065 * CPIM + C
Where Lift is defined as Condenser Saturated Refrigerant Temperature minus Evapora-
tor Saturated Refrigerant Temperature in °F . The CPIM is the average impeller diameter
in inches times 100.
High Lift Unloading Solenoid
The normally open contact of a AdaptiView control relay powers the normally closed
high lift unloading valve solenoid with the following logic:
High Lift Unloading
LLID Relay
State
De-energized De-energized
Energized Energized
The high lift unloading valve opens if the compressor is running and the IGV position
is at or below the Trigger IGV% line
– 5%. The high lift unloading valve closes when the IGV position reaches the Trigger
IGV% + 5% or the compressor shuts down.
Note that this 5% is of the full IGV travel range of 100%. Also note that operation of the
high lift unloading valve is independent of the high lift unloading limit mode as stated
below.
High Lift Unloading Limit Mode
For a Gear Drive chiller, the minimum IGV position is 60% of the Trigger IGV%. When
the IGV movement is being limited to the 60% of the Trigger IGV% point, the high lift
unloading limit submode is displayed.
Compressor Start Up
At compressor startup, the chiller is initialized as to not be in high lift unloading. The
rules to enter high lift unloading mode are as stated above. Also at startup, sufficient
time should be allowed so that an accurate Trigger IGV% may be calculated. Here
non-saturated conditions exist right away resulting in unstable temperature measure-
ments.
Manual Capacity Control
This is the Compressor Control Signal mode override in Large display ™. Here high
lift unloading solenoid valve operation, 60% of the Trigger IGV% and displaying of the
high lift unloading limit submode is obeyed.
Chiller Shutdown
The high lift unloading valve is normally closed (de-energized). There is no check per-
formed to ensure the valve is closed without using UT ™.
CVGF-SVX03B-EN
Valve Solenoid
Machine Protection and Adaptive Control
High Lift
Unloading Valve
Closed
Open
Function
No condenser gas bypass
Bypass condenser gas
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