FORM 150.60-NM4
YORK INTERNATIONAL
79
LD02099
FIG. 31
PIPING DIAGRAM
HOT GAS BYPASS (LOADMINDER) OPTION
General
The Hot Gas Bypass Option is available as a factory
installed option to prevent compressor cycling and wa-
ter temperature fluctuation at low load. This is ac-
complished by providing further capacity reduction be-
low the last step of compressor cylinder unloading by
introducing an artificial load to the cooler, which keeps
the compressor on the line. The option will provide hot
gas bypass on both compressors enabling hot gas to be
active regardless of which compressor is in the lead.
NOTE: The microprocessor will only activate the hot gas
on the lead compressor.
The hot gas bypass consists of a pilot operated regu-
lating valve with an integral solenoid. The pilot operated
solenoid is controlled by the microprocessor according
to water temperature. The regulating valve which becomes
activated when the solenoid is energized, is controlled
by suction pressure to modulate the flow of gas in a
bypass connected from the compressor discharge to the
cooler inlet. The following text will explain how the hot
gas solenoid is activated by the microprocessor in both
return and in leaving water control.
LWT Control Hot Gas Operation
The hot gas solenoid is energized when the leaving wa-
ter temperature falls below the Target water temperature,
if the compressor is on its minimum stage of loading.
Hot gas may then be fed according to the suction pres-
sure and the pressure regulating valve setting. Once ac-
tivated, the micro will keep the solenoid energized until
the leaving water temperature rises above the high limit
of the Control Range or until the load becomes so low
that the hot gas can no longer keep temperature within
the control range and the micro turns the compressor
off. Details for setting the pressure regulator follow.
RWT Control Hot Gas Operation
The hot gas solenoid is energized if the compressor is
on its minimum stage of loading and the return water
temperature falls below the following point:
ULCR - CR + CR/20
Where: UCLR = Upper Limit of Control Range
CR = Control Range Differential
Example: In a typical system that requires a 45°F
leaving water temperature, we will have a
10° control range (CR) differential which
gives us an Upper Limit of Control Range
(ULCR) of 55°F. Therefore, plugging the
numbers into the formula:
55 - 10 + (10/20) = 45-1/2°F
The hot gas solenoid will be activated at 45-1/2°F in the
example above and hot gas may then be fed according
to the suction pressure and the pressure regulated valve
setting. Once activated, the micro will keep the solenoid
energized until the return water temperature rises above
the temperature designated by the formula:
ULCR - CR + CR/10
Where: UCLR = Upper Limit of Control Range
CR = Control Range Differential
Example: 55 - 10 + 10/10 = 46°F
If temperature continues to drop while the Hot Gas is
energized, the Hot Gas will be de-energized when the
compressor cycles off on temperature.
Procedure For Setting The Hot Gas Regulator
(Ref. Fig. 31)
1. If desired, set the control panel data to show suction
pressure.
2. Adjust the pilot power assembly adjustment screw
2 to approximately the middle of its adjustment
range.
3. The chiller must be running and stabilized on the
minimum stage capacity. In establishing this condi-
tion, it may be necessary to deactivate the regulator
by de-energizing the solenoid 1 .
4. Adjust the adjustment screw 2 in the clockwise
direction to open the valve at a higher pressure
(sooner) or in the counterclockwise direction to open
the valve at a lower pressure (slower response). The
valve is feeding when the valve outlet feels warm to
the touch.
The adjustment is correct when system suction pres-
sure rises to a point nearly equal to normal running
pressure at the midpoint in the Control Zone.
