York Millennium YCAS 310, Installation Operation & Maintenance

Page: 105 / 124

FORM 201.10-NM3
105
YORK INTERNATIONAL
and unloading of the two groups will occur. This
assures that the chiller will fully load and main-
tain chilled liquid temperature.
NOTE: Viewing % FLA or % Slide Valve of each com-
pressor can often show a significant difference
in the value for each compressor even though
load equalization should occur. This is usually
due to small pressure and mechanical variations
in each system causing each compressor to load
or unload a different amount with a load or un-
load signal of a specific duration. Any differences
will normally be readjusted in time, but regard-
less of any difference in % FLA or % Slide Valve,
the micro will still assure that leaving chilled liq-
uid temperature is properly controlled.
Lag Compressor Differential Off
On falling demand for cooling, the Lag Compressor Dif-
ferential Off % decides the overall load level below
which equal load sharing will be stopped. This load level
is calculated as the Lag Compressor Start Point % mi-
nus the Lag Compressor Differential Off %. Below this
level of loading, the lead compressor maintains its load-
ing while the lag compressor continues to unload and,
if necessary, shut down. The lead compressor loading
will then be adjusted to maintain correct liquid tempera-
ture control.
The micro will accept a range of programmable values
between 0 - 50% for this control, provided the Lag Com-
pressor Start Point % minus the Lag Compressor Dif-
ferential Off % is not less than 20%. This is calculated
by the micro and an “Out of Range” message will be
displayed if this condition is not satisfied.
Larger % differential values increase chiller efficiency
by keeping the lag compressor operating on equalized
loading over a wide load range, which makes more ef-
ficient the use for the chiller heat exchangers. Cycling
of the lag compressor will also be minimized. For effi-
ciency purposes a setting of 50% is recommended.
A small % differential will increase cycling and lower
efficiency slightly but will minimize overall compressor
running time.
To program the Lag Compressor Differential Off %, key
in the required setting and press the Enter key to store
the value into memory and scroll to the next display.
L A G C O M P R E S S O R
D I F F E R E N T I A L O F F 3 0 %
Fan Control Discharge Pressure Setpoint
When a compressor starts, the discharge pressure be-
gins to rise. The Fan Control Discharge Pressure Set-
point is the discharge pressure at which the first stage
of condenser fan operation begins. If compressor load
increases and discharge pressure continues to rise,
then at 20 PSI above the FAN CNTRL DSCH SET-
POINT, the second stage of fan operation begins. If
more cooling is required, then at 40 PSI above the set-
ting the third and final stage of fan operation begins.
The Fan Control Discharge Pressure Setpoint is pass-
word protected.
The micro will accept programmable values between 149
- 351 PSIG on R22 models and between 72 - 203 PSIG
on R134a models for this set point. A low setting will
give most efficient operation of the chiller by minimizing
discharge pressure, however, too low a setting will cause
oil to return and expansion valve problems which could
cause damage to the compressor. The recommended
point of fan starting for most applications is 230-270 PSIG
for R22 models or 102-XXX PSIG for R134a models.
To program the Fan Control Discharge Pressure Set-
point, key in the required setting and press the Enter
key to store the value into memory and scroll to the
next display.
Fan On/Off Differential Pressure
On falling discharge pressure the Fan On/Off Pressure
Differential determines the “Off” pressure at which each
stage of fan operation will cycle off. The off pressure of
each stage is calculated as the start pressure for that
stage of fans (see above) minus the differential. When
all fans have stopped, restart will not occur until dis-
charge pressure again rises to the Fan Control Dis-
charge Pressure Setpoint.
A Fan On/Off Pressure Differential setting of 50 - 70
PSI is recommended.
To program the Fan On/Off Pressure Differential, key
in the required setting and press the Enter key to store
the value into memory and scroll to the next display.
Compressor Motor FLA Setting
F A N C N T R L D S C H P R E S S
S E T P O I N T = 2 3 0 P S I G
F A N O N / O F F P R E S S
D I F F = 5 0 P S I G
S Y S T E M # M O T O R C U R R
1 8 3 A M P S = 1 0 0 % F L A